OCR A-Level Physics Revision
Explore OCR A-Level Physics revision topics. Check the official specification for complete requirements for your exam year and route.
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OCR A-Level: Physics A (H556)
Exam years · 2027Specification version · Version 3.0 (March 2026)
Course details
Assessment For assessment details, see the official specification.
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Reviewed course guidance
Revision points, with the explanation beside them
Open a point to read what to know, how to use it in an assessment, a plain-language explanation and a self-check. Answers stay hidden until you choose to reveal them.
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Topic group
Reviewed requirements
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §1.1.1(a)-(c)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- A practical design turns a physical model into a measurable question: identify the variable changed, the response measured, useful range, apparatus and repeat strategy. Control a variable when it could independently alter the response.
- A method is appropriate only if its resolution, range and controls can distinguish the predicted effect from scatter or bias.
What to do in an assessment
- Predict the relationship first, then choose instruments and a sequence that measure it. State each control and how it is held fixed.
- For a spring test, load the same spring in increments, measure extension from its unloaded length, and keep temperature and loading history consistent.
In plain language
Good practical work tests a model, not just produces numbers.
Self-check
Why repeat each load and use the same spring?
Show the answer
Repeats reveal scatter; keeping the spring fixed avoids changing its spring constant.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §1.1.2(a)-(c); 1.1.3(a)-(d)(i)-(ii)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Choose analogue or digital apparatus for quantity and resolution; check zero, use correct units, and record raw observations consistently. Process data with appropriate mathematics and significant figures.
- Graph the independent variable horizontally, label quantity and unit, choose a scale, then use the best-fit gradient/intercept to test the model.
What to do in an assessment
- Measurement and analysis should be reproducible: preserve raw data and explain how a fitted graph represents the physical relationship.
- On an extension-against-force graph, gradient is extension per force; in a Hookean range its reciprocal is stiffness.
In plain language
A useful graph is a model test, not decoration.
Self-check
Why can a best-fit gradient be better than using two raw points?
Show the answer
It represents the overall trend and reduces the influence of individual scatter; calculate using two well-separated points on the fitted line.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §1.1.4(a)-(e); 2.2.1(a)-(d)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Systematic errors, including zero errors, bias readings; random variation produces spread. Precision concerns repeatability, accuracy closeness to accepted value. Absolute and percentage uncertainty quantify measurement limits.
- Inspect anomalies, error bars and method limitations. Identify the dominant uncertainty and improve the apparatus or procedure that causes it.
What to do in an assessment
- Repeats can improve confidence in random variation but cannot by themselves remove a shared systematic bias.
- Timing one oscillation by hand has a large reaction-time fraction; timing many reduces that contribution per period, but not a faulty clock calibration.
In plain language
Uncertainty determines how much confidence a measured result deserves.
Self-check
Does repeatedly measuring the same value prove accuracy?
Show the answer
No. It may show precision while a common zero or calibration error shifts every reading.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §1.2.1(a)-(j); 1.2.2(a)-(l)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- OCR names analogue and digital measurement, multimeters, timing, calipers/micrometers, circuit building, signal generators and oscilloscopes, wave apparatus, lasers/light sources, ICT/data loggers and ionising-radiation detectors.
- Choose instruments from the measured quantity; state risk controls, record observations, process with suitable tools, cite research and retain enough records for another person to reconstruct the work.
What to do in an assessment
- Read an oscilloscope trace by multiplying horizontal divisions by the time-base, then take the reciprocal for frequency.
- Match the meter, range and resolution to the quantity; check zero/polarity and state radiation or electrical safeguards.
In plain language
An oscilloscope gives voltage against time: period equals horizontal divisions times time-base per division, and frequency is its reciprocal.
Self-check
A trace spans 4.0 divisions at 0.50 ms per division. What frequency is shown?
Show the answer
T=2.0 ms, so f=500 Hz, assuming the trace and time-base are read correctly.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §1.2.2(a)-(l); 5g Table 1 PAG1-PAG12
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- PAGs are: motion; material properties; electrical properties; circuits; waves; quantum effects; ionising radiation; gases; capacitors; simple harmonic motion; investigative/unscaffolded work; research skills. The source calls for at least 12 assessed practicals across the required experience.
- Explain variables, risk, apparatus, raw-data handling, processing, uncertainty and conclusion for each experiment. The separate teacher-assessed endorsement uses CPAC and is reported independently of written-paper marks.
What to do in an assessment
- Choose a suitable activity for each PAG and list the apparatus, variables, measurements and hazards before work.
- Record raw data and show processing, uncertainty, conclusion and source citations; check against the relevant CPAC.
In plain language
A PAG is a required field of practical experience, not one single compulsory recipe; centres can choose suitable contexts that build the listed techniques.
Self-check
Does writing about a PAG in an exam prove the practical endorsement has been passed?
Show the answer
No. Written papers assess practical knowledge; Component 04 is separately assessed against practical criteria.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §2.1.1(a)-(b); 2.1.2(a)-(f)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Every quantity is a number and unit. Use SI base/derived units and decimal prefixes; estimate plausible magnitudes and check dimensions on both sides of an equation.
- Convert prefixes before substitution and derive units from definitions: N=kg m s⁻², J=N m. Label graph axes as quantity per unit.
What to do in an assessment
- Convert quantities to SI before substitution, applying squared/cubed prefixes correctly.
- Derive the units from each equation and compare dimensions on both sides before calculating.
In plain language
Dimensional analysis catches impossible equations before arithmetic does.
Self-check
What unit follows for momentum from p=mv?
Show the answer
kg m s⁻¹, from mass multiplied by velocity.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §2.3.1(a)-(d)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Scalars have magnitude only; displacement, velocity, acceleration and force are vectors. Vectors add head-to-tail; subtraction adds the opposite vector.
- Choose axes, resolve with sine/cosine, keep signs, then use Pythagoras and inverse tangent for resultant magnitude and direction.
What to do in an assessment
- Resolve each vector into signed horizontal and vertical components using sine and cosine.
- Add the components, then calculate resultant magnitude and direction with Pythagoras and inverse tangent.
In plain language
A projectile’s horizontal and vertical motions are components of one velocity but can be analysed independently.
Self-check
What result follows from this task: Resolve a 10 N force 30° above horizontal.
Show the answer
Fx=10cos30°=8.66 N; Fy=10sin30°=5.00 N.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.1.1(a)-(d)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Average velocity is displacement/time; instantaneous velocity is the gradient of displacement-time at one instant. Velocity-time gradient is acceleration and signed area is displacement.
- Distinguish distance from displacement and use tangent gradients for instantaneous quantities. Check axis units before interpreting a slope or area.
What to do in an assessment
- Use a tangent for instantaneous gradient and calculate signed area under a velocity-time graph.
- Compare displacement and distance separately when velocity changes sign.
In plain language
A velocity graph crossing zero signals reversal; signed areas can cancel although distance remains positive.
Self-check
What result follows from this task: Velocity is +3 m s⁻¹ for 4 s then −3 m s⁻¹ for 4 s. Give displacement and distance.
Show the answer
Displacement is 0 m; distance is 24 m.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.1.2(a)(i)-(ii); 3.1.2(b)(i)-(ii)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- For constant acceleration: v=u+at, s=ut+½at² and v²=u²+2as. Near Earth, free-fall acceleration g is approximately constant; air resistance may invalidate ideal free-fall assumptions.
- Choose an equation without the unknown, define positive direction and use coherent SI units. Determine g from repeated position/time or velocity/time data and explain timing and drag limits.
What to do in an assessment
- Select a constant-acceleration equation that excludes the unknown and define a positive direction.
- Determine g from repeated motion measurements; explain the timing resolution and drag assumptions.
In plain language
Starting from rest, an ideal fall for 0.50 s covers ½gt²≈1.23 m.
Self-check
What result follows from this task: Speed changes from 4 to 16 m s⁻¹ in 3.0 s. Find acceleration.
Show the answer
a=(16−4)/3.0=4.0 m s⁻².
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.1.2(c)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Thinking distance is the distance travelled during reaction time; braking distance is travelled while the brakes slow the vehicle. Stopping distance is their sum.
- At fixed reaction time thinking distance scales with speed; ideal braking distance increases with speed squared for fixed deceleration. Separate terms in safety calculations.
What to do in an assessment
- Calculate thinking distance as speed multiplied by reaction time.
- Add the separately modelled braking distance and explain how speed, road and tyre conditions affect it.
In plain language
At 20 m s⁻¹ and 0.7 s reaction time, thinking distance is 14 m before braking.
Self-check
What is thinking distance at 20 m s⁻¹ and 0.7 s?
Show the answer
d=vt=14 m.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.1.3(a)-(b)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Ignoring drag, gravity changes vertical velocity while horizontal velocity stays constant; both components share the same time.
- Resolve launch velocity, solve vertical motion for flight time, then use that time for horizontal displacement. State when air resistance matters.
What to do in an assessment
- Resolve launch velocity into horizontal and vertical components.
- Find flight time from vertical motion, then use the same elapsed time to calculate horizontal displacement.
In plain language
A horizontal launch begins with zero vertical velocity but immediately accelerates downward at g.
Self-check
A ball travels horizontally at 12 m s⁻¹ for 0.40 s. How far?
Show the answer
x=vt=4.8 m if drag is negligible.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.2.1(a)-(f); 3.2.2(a)-(d)(i)-(ii)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Newton’s second law is resultant force F=ma; weight is mg. A free-body diagram shows forces acting on one chosen object. Drag opposes relative motion through a fluid and depends on factors such as speed, shape and area.
- At terminal velocity, drag and other opposing forces balance weight: resultant force and acceleration are zero. Measure changing speed to identify the plateau and evaluate fluid/shape controls.
What to do in an assessment
- Draw a free-body diagram for the chosen falling body and write the signed resultant force.
- Use speed-time measurements to identify terminal velocity and explain which forces balance there.
In plain language
An object at terminal velocity can move quickly: zero acceleration does not mean zero velocity.
Self-check
What result follows from this task: A 2.0 kg body falls at terminal speed with negligible buoyancy. Find drag.
Show the answer
D=mg=19.6 N upward.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.2.3(a)-(f); 3.2.4(a)-(c)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Moment is force times perpendicular distance; a couple has torque Fd. Equilibrium requires zero resultant force and torque. Density ρ=m/V, pressure p=F/A, fluid pressure difference p=ρgh and Archimedes’ principle links upthrust to displaced-fluid weight.
- Use perpendicular lever arms and compare clockwise/anticlockwise moments. Find centre of gravity by intersecting plumb lines; use consistent units in pressure and density calculations.
What to do in an assessment
- Take moments about a named pivot using perpendicular lever arms and test rotational equilibrium.
- Calculate p=F/A or ρgh with SI units and relate upthrust to displaced-fluid weight.
In plain language
A small force far from a pivot can balance a large one near it; floating depends on displaced-fluid upthrust.
Self-check
A 12 N force acts 0.30 m from a pivot. What force at 0.20 m balances it?
Show the answer
F×0.20=12×0.30, so F=18 N in the opposite rotational sense.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.3.1(a)-(e); 3.3.2(a)-(c); 3.3.3(a)-(c)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Work W=Fs cosθ transfers energy; energy is conserved across forms. Kinetic energy is ½mv², near-Earth gravitational energy mgh, power is energy per time and P=Fv when force is parallel to velocity. Efficiency is useful output/total input.
- Choose a system boundary and account for useful and dissipated energy. For a lift calculate mgh/t; compare useful output with input to find efficiency.
What to do in an assessment
- Choose a system boundary and account for each energy store and transfer.
- Calculate work, energy, power or efficiency from the relevant source equation and state where dissipated energy goes.
In plain language
Energy can be conserved while a device is inefficient because some energy is dissipated into unwanted surroundings.
Self-check
What result follows from this task: A 60 kg person climbs 3.0 m in 5.0 s. Find gain in gravitational power.
Show the answer
P=mgh/t≈353 W.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.4.1(a)-(d)(i)-(ii); 3.4.2(a)-(f)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Hooke’s law F=kx applies in the proportional range. Graph area gives work; spring energy is ½kx². Stress=F/A, strain=extension/original length and Young modulus=stress/strain.
- Use force-extension and stress-strain curves to identify elastic/plastic behaviour, stiffness, ultimate tensile strength and material class. Determine E from measured wire dimensions and slope; note diameter uncertainty is squared in area.
What to do in an assessment
- Plot force against extension and identify the proportional range and graph area.
- Calculate stress, strain and Young modulus from wire force, extension, original length and cross-section.
In plain language
Permanent deformation remains after unloading; elastic deformation reverses.
Self-check
What result follows from this task: A 2.0 m wire extends 1.0 mm under stress 1.0×10⁸ Pa. Find E.
Show the answer
Strain=5.0×10⁻⁴, so E=2.0×10¹¹ Pa.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.5.1(a)-(e); 3.5.2(a)-(c)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Momentum p=mv is a vector; resultant force is rate of change of momentum. Impulse FΔt equals momentum change and area under a force-time graph. Isolated systems conserve momentum; elastic collisions also conserve kinetic energy.
- Set a system and signed direction, equate momentum before and after, and use force-time area for variable interactions. Explain how longer impact time reduces average force.
What to do in an assessment
- Choose the interacting system and sign convention, then equate total momentum before and after.
- Use the area of a force-time graph for impulse and connect longer collision time with lower average force.
In plain language
Two moving carts can have zero total momentum if their momenta are equal and opposite.
Self-check
What result follows from this task: A 0.20 kg ball changes velocity from +5 to −3 m s⁻¹. Find impulse.
Show the answer
Δp=0.20(−3−5)=−1.6 N s.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.1.1(a)-(g); 4.1.2(a)-(c)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Current I=ΔQ/Δt; charge is quantised in units of elementary charge e. Conventional current is opposite electron drift in metals. I=Anev relates current to carrier density, charge and mean drift speed.
- Use Q=It for steady current and N=Q/e for elementary charges. Distinguish carrier motion from conventional current; compare mobile carrier density in conductors, semiconductors and insulators.
What to do in an assessment
- Use Q=It and N=Q/e for a steady current; label conventional-current direction separately from electron drift.
- Use I=Anev to link carrier density, cross-section and drift speed, keeping each unit consistent.
In plain language
The electric effect propagates quickly although individual electrons drift slowly.
Self-check
What result follows from this task: A 2.0 A current flows for 30 s. Find charge and electron count.
Show the answer
Q=60 C; N≈60/(1.6×10⁻¹⁹)=3.75×10²⁰.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.2.1(a)-(b); 4.2.2(a)-(e); 4.2.3(a)-(d); 4.2.4(a)-(c); 4.2.5(a)-(c)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Potential difference is energy transferred per charge; emf is energy supplied per charge by a source. Ohm’s law holds at constant physical conditions; resistivity R=ρL/A. Filament lamps, LDRs and thermistors are non-ohmic.
- Use I–V graphs to test proportionality. Determine resistivity from V/I and specimen geometry. Calculate P=VI=I²R=V²/R, W=VIt, and household energy/cost in kWh.
What to do in an assessment
- Use an I-V graph to decide whether a component is ohmic and determine resistance/resistivity.
- Calculate circuit power and energy, converting kilowatt-hours to cost only after finding energy use.
In plain language
A filament warms, its resistance rises and its I–V curve bends.
Self-check
What result follows from this task: A 12 V resistor carries 0.50 A for 2 min. Give power and energy.
Show the answer
P=6.0 W; W=6.0×120=720 J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.3.1(a)-(f); 4.3.2(a)-(c)(i)-(ii); 4.3.3(a)-(c)(i)-(ii)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Kirchhoff’s first law conserves charge at junctions; the second conserves energy around loops. Series resistances add; parallel reciprocals add. A real source obeys E=V+Ir, and dividers split voltage by resistance.
- Label currents and polarities before solving loops. Measure V against I to determine internal resistance; model sensor dividers at both extremes to check output range.
What to do in an assessment
- Label currents and voltage polarities, then apply Kirchhoff rules with series/parallel equivalents.
- Calculate loaded terminal voltage or divider output at sensor extremes to check circuit behaviour.
In plain language
Loaded-cell terminal voltage falls below emf because some energy is transferred inside the source.
Self-check
What result follows from this task: A 6.0 V source with 1.0 Ω internal resistance supplies 2.0 A. Find terminal voltage.
Show the answer
V=E−Ir=4.0 V.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.4.1(a)-(g); 4.4.2(a)-(e); 4.4.3(a)-(g); 4.4.4(a)-(g)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Progressive waves transfer energy; f=1/T and v=fλ. Reflection, refraction, diffraction and polarisation are wave behaviours. For light n=c/v. Superposition gives constructive/destructive interference; standing waves have nodes/antinodes separated by λ/2.
- Use normals for refraction angles and relate path difference to phase. In a double slit λ=ax/D; use resonance patterns to infer sound wavelength/speed.
What to do in an assessment
- Use v=fλ and n=sin i/sin r with angles measured from the normal.
- Predict constructive/destructive interference from path difference; use fringe spacing or standing-wave separation to calculate λ.
In plain language
Standing waves arise when waves of the same frequency travel oppositely and interfere.
Self-check
What result follows from this task: Slit separation 0.30 mm, screen distance 1.5 m, fringe spacing 3.0 mm: estimate λ.
Show the answer
λ=xd/D=6.0×10⁻⁷ m.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.5.1(a)-(e)(i)-(ii); 4.5.2(a)-(f); 4.5.3(a)-(c)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Photon energy E=hf=hc/λ. Photoelectric emission is a one-photon/one-electron interaction; hf=φ+Kmax explains threshold frequency and why maximum kinetic energy depends on frequency, not intensity. Electron diffraction supports particle waves, λ=h/p.
- Convert eV to joules before combining units; distinguish photon energy from photon flux. Use photoelectric data versus frequency to infer h and work function.
What to do in an assessment
- Use E=hf and φ+Kmax=hf to distinguish photon frequency from intensity effects.
- Convert eV to joules where needed and apply λ=h/p to a moving particle.
In plain language
Above threshold, more intensity raises emission rate, not maximum kinetic energy of each electron.
Self-check
What result follows from this task: Find energy of a 5.0×10¹⁴ Hz photon.
Show the answer
E=hf=3.32×10⁻¹⁹ J, about 2.07 eV.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.1.1(a)-(d); 5.1.2(a)-(g); 5.1.3(a)-(d)(i)-(ii); 5.1.4(a)-(i)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Temperature sets thermal equilibrium; Kelvin is absolute (T/K≈θ/°C+273). Particle models explain phase, Brownian motion and internal energy. Specific heat capacity gives Q=mcΔT; latent heat Q=mL changes phase without temperature rise.
- For ideal gases use pV=NkT or nRT and absolute pressure/temperature. Explain pressure as momentum transfer and connect mean kinetic energy per molecule to temperature.
What to do in an assessment
- Choose Q=mcΔT for temperature change or Q=mL for phase change.
- Use pV=nRT with kelvin and absolute pressure; explain pressure through wall-collision momentum transfer.
In plain language
During melting, energy separates particles rather than raising average kinetic energy, so temperature can remain constant.
Self-check
What result follows from this task: Heat 0.20 kg with c=900 J kg⁻¹ K⁻¹ by 15 K.
Show the answer
Q=mcΔT=2700 J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.2.1(a)-(c); 5.2.2(a)-(d)(i)-(ii)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Radian angle is arc length/radius; angular velocity ω=2πf, linear speed v=ωr and centripetal acceleration v²/r=ω²r. The inward resultant force is mv²/r.
- Convert period to frequency first and identify which interaction supplies centripetal force. Do not draw an invented outward force.
What to do in an assessment
- Convert period to frequency and calculate ω=2πf and v=ωr.
- Identify the inward physical force and use a=v²/r or F=mv²/r.
In plain language
Constant speed in a circle still means acceleration because velocity direction changes.
Self-check
What result follows from this task: A 0.40 kg mass moves at 3.0 m s⁻¹ on radius 0.60 m. Find inward force.
Show the answer
F=mv²/r=6.0 N.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.3.1(a)-(g); 5.3.2(a)-(b); 5.3.3(a)-(e)(i)-(ii)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- SHM has a=−ω²x. For a spring T=2π√(m/k); for a small-angle pendulum T=2π√(l/g). Kinetic and potential energies exchange; damping removes energy and forced amplitude peaks near resonance.
- Use displacement, velocity and acceleration graphs to compare phase; explain the effects of driving frequency and damping.
What to do in an assessment
- Use a=−ω²x to determine acceleration direction and identify phase from x, v and a graphs.
- Calculate spring or pendulum period from its source conditions, then explain damping and resonance.
In plain language
At maximum displacement, speed is zero and restoring acceleration is largest; at equilibrium, speed is largest.
Self-check
What result follows from this task: A 0.50 kg mass is attached to k=200 N m⁻¹. Find period.
Show the answer
T=2π√(0.50/200)≈0.314 s.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.4.1(a)-(e); 5.4.2(a)-(c); 5.4.3(a)-(e); 5.4.4(a)-(e)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Outside a spherical mass, model it as a point: F=GMm/r² and g=GM/r². Gravitational potential is work per mass, Vg=−GM/r. In an orbit gravity supplies centripetal force; Kepler links T²∝r³.
- Use distance from centre in inverse-square laws; equate gravity and centripetal force for circular orbits. Escape speed leaves zero kinetic energy at infinity.
What to do in an assessment
- Use centre-to-centre radius in inverse-square field/force calculations.
- Set gravitational force equal to centripetal force for a circular orbit and apply T²∝r³ for comparisons.
In plain language
Field points toward mass but potential relative to zero at infinity is negative.
Self-check
What result follows from this task: Compare field strengths at radii R and 2R.
Show the answer
g(2R)=g(R)/4.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.5.1(a)-(g); 5.5.2(a)-(k); 5.5.3(a)-(o)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Spectral lines mark quantised electron energy changes; stellar spectra reveal composition and temperature. HR diagrams organise luminosity and temperature; low-mass stars become white dwarfs and massive stars can form neutron stars or black holes. Wien and Stefan laws relate temperature, peak wavelength, luminosity and radius.
- Use parallax for distance, redshift for recession and Hubble’s law for expansion; convert units carefully and distinguish evidence from a model’s inference.
What to do in an assessment
- Use Wien or Stefan relationships with correct temperature and wavelength units.
- Use parallax, redshift or Hubble data to infer quantities while stating model assumptions.
In plain language
A redshift is evidence of recession in the relevant model, not a direct image of a primordial event.
Self-check
What result follows from this task: For λmax=5.0×10⁻⁷ m and Wien constant 2.90×10⁻³ m K, estimate T.
Show the answer
T=5.8×10³ K.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.1.1(a)-(e); 6.1.2(a)-(c); 6.1.3(a)-(e)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Capacitance C=Q/V; parallel capacitances add, series reciprocals add. Stored energy is area under a Q–V graph or ½QV. An RC time constant τ=RC sets exponential charging/discharging; after one τ discharge leaves 1/e of initial voltage.
- Identify initial/final levels and τ from a trace; plot ln(V) against time for discharge slope −1/RC.
What to do in an assessment
- Find total capacitance using the correct series or parallel rule and calculate stored energy.
- Determine τ=RC or fit a log-voltage/time graph to test exponential discharge.
In plain language
Capacitor voltage changes exponentially, not by the same amount each second.
Self-check
What result follows from this task: A 100 μF capacitor discharges through 20 kΩ. Find τ.
Show the answer
τ=RC=2.0 s.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.2.1(a)-(d); 6.2.2(a)-(d); 6.2.3(a)-(b); 6.2.4(a)-(e)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Coulomb force varies with charge product and inverse-square distance. Field strength is force per positive unit charge; potential is energy per unit charge. Between parallel plates E=V/d; electric and gravitational fields share inverse-square structure, but electric forces can attract or repel.
- Track sign: an electron force is opposite electric field. Use field diagrams, potential differences and energy QV consistently.
What to do in an assessment
- Draw the electric-field direction and determine the force direction from the sign of charge.
- Calculate field, potential-energy transfer or force with signs, geometry and units shown.
In plain language
Field direction is defined by a positive test charge; a negative charge accelerates opposite it.
Self-check
Move 2.0 μC through 5.0 V. Energy transferred?
Show the answer
ΔE=QV=1.0×10⁻⁵ J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.3.1(a)-(f); 6.3.2(a)-(e); 6.3.3(a)-(g)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Current produces magnetic field; moving charges/current-carrying conductors experience magnetic force. Flux Φ=BAcosθ; changing flux induces emf and Lenz’s law gives the opposing direction.
- For a charge perpendicular to B, equate |q|vB to mv²/r. For coils, induced emf magnitude follows rate of flux-linkage change.
What to do in an assessment
- Use a consistent right-hand rule and identify what change in flux linkage produces induced emf.
- For perpendicular motion use |q|vB=mv²/r; for induction use flux-change rate and Lenz direction.
In plain language
A steady field through a stationary coil induces no emf unless linked flux changes.
Self-check
What result follows from this task: An electron at 2.0×10⁶ m s⁻¹ crosses 0.010 T perpendicularly. Find force magnitude.
Show the answer
F=|q|vB=3.2×10⁻¹⁵ N.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.4.1(a)-(g); 6.4.3(a)-(h); 6.4.4(a)-(k)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Nuclear equations conserve proton/nucleon number. Binding energy per nucleon indicates stability; ΔE=Δmc² accounts for fission/fusion energy. Alpha, beta and gamma differ in ionisation and penetration; activity decays exponentially and individual decays are random.
- Balance nuclear equations; use half-life or exponential models. Distinguish absorbed dose in gray from effective dose in sievert and discuss risk.
What to do in an assessment
- Balance proton/nucleon numbers and use binding-energy or decay evidence for stability.
- Calculate activity/half-life and distinguish absorbed dose in gray from effective dose in sievert.
In plain language
Activity is decays per second; it is not by itself the same as absorbed dose in a person.
Self-check
An 800 Bq sample has 6 h half-life. Activity after 18 h?
Show the answer
Three half-lives: 800/8=100 Bq.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.5.1(a)-(c); 6.5.2(a)-(e); 6.5.3(a)-(e)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- X-rays attenuate by absorption and scattering; tissue contrasts create detector patterns. Ultrasound echoes reflect at acoustic-impedance boundaries; CT reconstructs cross-sections from multiple X-ray projections.
- For pulse echo use depth=cΔt/2. Compare image resolution, contrast, dose and hazards; explain how measured signal becomes an image.
What to do in an assessment
- Trace how transmitted X-rays, echoes or tomographic projections become image contrast.
- For pulse-echo ultrasound calculate depth=cΔt/2 and compare image resolution, contrast and dose.
In plain language
A CT slice is reconstructed from many angular projections, not a single shadow.
Self-check
What result follows from this task: An ultrasound echo returns in 80 μs; sound speed is 1.5×10³ m s⁻¹. Find depth.
Show the answer
d=cΔt/2=0.060 m.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5e M0-M4; 5d HSW1-HSW12
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- H556 assesses units, estimates, standard form, ratios, trig, data, significant figures, uncertainty, algebra, graphs, areas, gradients, vectors, radians and geometry in physics contexts. HSW covers models, questions, methods/risk, evidence, evaluation, development of knowledge, communication, application, ethics, validation and decisions.
- Check dimensions and magnitude; propagate uncertainty according to operations. Compare models to evidence, identify correlation/causation limits and communicate claim, reasoning and caveats.
What to do in an assessment
- Show dimensional checks, suitable significant figures and uncertainty propagation in a physics calculation.
- Compare a model with evidence, identify uncertainty and communicate a conclusion with limitations and risk context.
In plain language
A formula can be algebraically rearranged yet physically wrong if its units do not balance.
Self-check
Radius has 2% uncertainty. Approximate area uncertainty for A=πr²?
Show the answer
Approximately 4%, because relative uncertainty doubles when r is squared.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §2a; 3a; 3b; 3i; 3j
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- H556 papers: /01 Modelling physics, 100 marks, 2 h 15 min, 37%; /02 Exploring physics, 100 marks, 2 h 15 min, 37%; /03 Unified physics, 70 marks, 1 h 30 min, 26%. /01 assesses Modules 1,2,3,5; /02 Modules 1,2,4,6; /03 all six modules.
- On /01 and /02, Section A is 15 marks of multiple-choice questions and Section B is 85 marks of structured responses, including problems, calculations, practical/data questions and extended responses. /03 is a 70-mark, 90-minute Unified Physics paper drawing on all six modules and can combine their question styles and content. All three written papers include synoptic assessment.
- AO1 assesses knowledge and understanding of scientific ideas, processes, techniques and procedures. AO2 assesses applying that knowledge and understanding in theoretical and practical contexts, including qualitative and quantitative data. AO3 assesses analysing, interpreting and evaluating scientific information, ideas and evidence, including making judgements and reaching conclusions, and developing and refining practical designs and procedures. Across the written assessment the approximate mark ranges are AO1 31–34%, AO2 40–43% and AO3 25–28%.
- The overall written grade is based on the combined marks from /01, /02 and /03, compared with the relevant overall grade boundaries. Component /04 Practical Endorsement is separately reported non-exam assessment; it is not added to those written marks.
What to do in an assessment
- Map each module to its listed paper, but prepare to connect ideas across modules in any written component. For example, use mechanics momentum and circular motion together with magnetic force, qvB=mv²/r, to explain a charged particle’s measured path radius; then identify how scale, repeat readings and uncertainty in the radius affect the result. This combines physics content with practical measurement and data evaluation.
- When interpreting a question, identify whether it asks you to recall/explain (AO1), apply a model to a context (AO2), or analyse evidence/evaluate a method (AO3); a single question can assess more than one objective.
- At grade time, add the marks for written components /01–/03 and compare that total with the applicable overall grade boundary. Keep the separately reported /04 Practical Endorsement out of this calculation.
In plain language
All three papers test physics, and the unified paper can connect modules; your written grade comes from the three paper marks together, not the separate Practical Endorsement.
Self-check
A student scores 72/100 on /01, 68/100 on /02 and 48/70 on /03. Which marks form the written total, and does an /04 Practical Endorsement pass add marks?
Show the answer
Add the three written marks: 72+68+48=188/270, then compare that total with the applicable overall grade boundaries. The separately reported /04 endorsement pass does not add written marks.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.4.2(a)-(l); 6.4.4(a)-(k)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Hadrons such as protons and neutrons experience strong and weak interactions; leptons such as electrons and neutrinos do not experience the strong interaction. Hadrons are modelled using u, d and s quarks; proton uud and neutron udd.
- Particle-antiparticle pairs, beta transformations, binding energy per nucleon, mass defect, ΔE=Δmc², fission chain reactions and fusion are distinct source outcomes.
What to do in an assessment
- Check charge conservation from quark charges; balance nuclear transformations and calculate energy from a measured mass defect.
- Explain fuel/control rods and moderator in a fission reactor, and weigh the environmental impact of waste against energy benefits.
In plain language
A quark model accounts for hadron composition while binding-energy change explains energy released in nuclear reactions.
Self-check
A reaction has a mass defect of 2.0×10⁻²⁹ kg. Estimate released energy.
Show the answer
ΔE=Δmc²=1.8×10⁻¹² J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.5.2(a)-(e)
This explanation covers part of the source requirement only. Its tick is separate and does not count as a fully revised requirement.
Open revision guidance
What to know
- Technetium-99m and fluorine-18 are medical tracers. A gamma camera uses a collimator, scintillator, photomultiplier tubes, computer and display. PET uses positron-electron annihilation and paired photons to reconstruct tracer distribution.
- Diagnosis depends on what the tracer reveals; scanner cost/availability and ionising exposure raise ethical and social decisions.
What to do in an assessment
- Trace the signal from tracer through detector to image; explain why gamma-camera collimation and PET coincidence information constrain source location.
- Compare diagnostic information and radiation risk rather than treating every scan as interchangeable.
In plain language
A tracer image maps radiopharmaceutical distribution; it is not simply an X-ray shadow of anatomy.
Self-check
Why are two photons useful in PET?
Show the answer
Annihilation produces oppositely directed photons; their coincident detection helps locate the event.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §1.1.1(a); §1.1.1(b); §1.1.1(c)
Open revision guidance
What to know
- Turn a physics question into a measurable independent variable, dependent variable and expected relationship. Select instruments, range and technique from the required resolution and range; use source physics to explain why those readings will answer the question.
- Identify variables that must be controlled because they could change the response, then evaluate whether the method can distinguish the predicted change from noise or bias.
What to do in an assessment
- Write a labelled method with apparatus, range, repeated readings, control values and risk controls. State how each variable is set or measured and how the observed pattern would test the model.
- For a spring extension investigation, load in increments, read extension from an unloaded reference, repeat each load and keep the same spring and temperature; reject a range that has already passed the elastic limit.
In plain language
An experiment is a model test with measurable variables and justified limits.
Self-check
How would you test whether extension is proportional to force over a stated range?
Show the answer
Measure repeated extensions at several forces for the same spring, control temperature and loading history, plot extension against force, and test whether the data remain linear through the origin within uncertainty.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §1.1.2(a); §1.1.2(b); §1.1.2(c)
Open revision guidance
What to know
- Use apparatus and techniques appropriate to the actual physical quantity and precision required; read scales at eye level, check zero and avoid over-ranging. Select a coherent unit before recording.
- A useful record separates raw observations from calculated values, labels quantities and units, and preserves enough detail to reconstruct the measurement.
What to do in an assessment
- Choose the least-count and range before taking data, note zero correction and read an analogue scale between divisions where justified. Record every raw reading with unit and instrument resolution before processing.
- For current and voltage, state meter mode/range and circuit position; retain raw pairs in a table with headings such as current / A and potential difference / V.
In plain language
Units and raw records let another person understand exactly what was measured.
Self-check
A micrometer reads 12.34 mm with a +0.03 mm zero error. What corrected reading should be recorded?
Show the answer
12.34−0.03=12.31 mm; retain the raw reading and record the zero correction and instrument precision.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §1.1.3(a); §1.1.3(b); §1.1.3(c); §1.1.3(d)(i); §1.1.3(d)(ii)
Open revision guidance
What to know
- Reduce repeated measurements to appropriate means or ranges, process with a relevant physical model, keep units through calculations and report justified significant figures. Compare the result with the question and state a conclusion supported by data.
- Plot an independent variable against the response with axes as quantity/unit, a useful even scale, uncertainty/error bars where relevant, and a best-fit line/curve. The gradient and intercept have physical meanings only after their units and model are identified.
What to do in an assessment
- For a linear relation y=mx+c, select well-separated points on the fitted line, calculate m=Δy/Δx with units, and interpret c. For a curve, estimate a local rate with a tangent and estimate area using strips or suitable geometry.
- For repeated timings, calculate the mean, show any conversion, compare scatter with the predicted trend, and round only at the end to match measurement precision.
In plain language
Processing explains what the data say and how strongly they support a model.
Self-check
On a velocity–time graph, what do gradient and signed area represent?
Show the answer
Gradient is acceleration; signed area is displacement. Include graph-axis units when calculating each result.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §1.1.4(a); §1.1.4(b); §1.1.4(c); §1.1.4(d); §1.1.4(e)
Open revision guidance
What to know
- A conclusion should match the data and uncertainty, identify anomalies without deleting them silently, and distinguish random scatter from systematic bias or zero error. Precision describes spread; accuracy describes closeness to a valid reference.
- Combine absolute uncertainties for sums/differences and percentage or fractional uncertainties for products/quotients and powers; compare error bars, best/worst lines and percentage difference without claiming unjustified statistical certainty.
What to do in an assessment
- Calculate a percentage uncertainty as absolute uncertainty divided by measured value ×100%; for independent readings added to find a length, add their absolute uncertainties. Identify the largest contribution before recommending an improvement.
- Change one method feature that addresses the dominant limit: use a fiducial marker for alignment, time many oscillations to reduce reaction-time fraction, or use a calibrated higher-resolution instrument for scale uncertainty.
In plain language
A trustworthy result includes a clear account of how uncertain and limited it is.
Self-check
A length is 50.0±0.5 mm. What is its percentage uncertainty, and would repeats remove a shared zero error?
Show the answer
(0.5/50.0)×100=1.0%. Repeats reduce random scatter but do not remove a systematic zero error shared by every reading.
- Core
Open revision guidance
What to know
- Practical work develops independent investigative planning; safe/correct equipment use with hazard identification and risk minimisation; following written instructions; accurate observation/measurement and appropriate records; scientific presentation of information/data; and appropriate software/research/reporting. Research must use suitable online/offline scientific sources and correctly cite them; instrument/technique selection must suit the physics knowledge and context.
- Hazard control is part of the method: identify radiation, electrical, thermal, optical or mechanical hazards before work, reduce exposure/energy and record the control used. Research claims need traceable source details; do not present another person’s text or data as your own.
What to do in an assessment
- Plan an investigation from a practical problem, follow the approved written sequence, use apparatus safely, record raw observations with units, preserve an experimental record, process/report with appropriate tools, distinguish evidence from interpretation, and cite source material. For a free-fall investigation, document release geometry, distance/time readings, controls, repeats, uncertainty and risk controls before drawing a conclusion.
- In a report, separate observations from interpretation, cite the source of a constant or design choice and describe a software transformation so the analysis can be reproduced.
In plain language
Good practical physics combines a safe method, reliable evidence and an honest report.
Self-check
What should a reproducible practical record contain beyond a final value of g?
Show the answer
The apparatus and calibration, procedure and controls, raw distances/times with units, repeats, processing and uncertainty, risk controls, result with conclusion, and cited sources.
- Core
Open revision guidance
What to know
- Analogue measurement covers length/distance, temperature, pressure, force, angle and volume, including interpolation; digital measurement includes multimeters for time, current, voltage, resistance and mass. Calipers and micrometers measure small distances.
- Use repeated oscillations, a fiducial mark, set square or plumb line to improve geometry/timing; use stopwatch/light gates correctly. Build and check DC circuits (including polarity), use signal generators/oscilloscopes with V/div and time-base, create and measure waves with microphones/speakers, ripple tanks, transducers or microwave/radio sources, use laser/light for interference/diffraction, ICT/data loggers/software, and radiation detectors safely. The course requires at least 12 assessed practical activities (Appendix 5g); these apparatus outcomes are practice and written-paper practical knowledge, not evidence that teacher-assessed CPAC competence has been achieved.
What to do in an assessment
- Interpolate between analogue marks only to a defensible fraction of a division; state resolution. Zero and set the multimeter mode/range before connection, place an ammeter in series and voltmeter in parallel, and verify polarity before energising.
- For an oscilloscope trace, calculate T=(horizontal divisions)(time/division), f=1/T; for a wave or diffraction practical record geometry, repeated fringe/spacing data, detector settings and uncertainty, and compare results with the predicted relation.
In plain language
Correct apparatus, setup and reading strategy determine whether the data are meaningful.
Self-check
A trace spans 4.0 horizontal divisions at 0.50 ms per division. Find its frequency.
Show the answer
T=4.0×0.50 ms=2.0 ms=2.0×10⁻³ s; f=1/T=500 Hz.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §2.1.1(a); §2.1.1(b)
Open revision guidance
What to know
- A physical quantity is a numerical value multiplied by a unit; number alone is not a measurement. Estimates are order-appropriate values informed by familiar scales and stated conditions.
- Estimate only quantities listed in the specification by decomposing them into measurable factors, then compare with a reference scale before calculation.
What to do in an assessment
- For a room, estimate volume by measuring approximate length×width×height; attach m³ and state the dimensions assumed. Check that an estimated speed or energy has the right order of magnitude before accepting calculator output.
- Keep units attached to each intermediate value and convert before combining quantities.
In plain language
A number becomes useful physics only when its unit and scale are clear.
Self-check
A lab is about 8 m by 6 m by 3 m. Estimate its volume.
Show the answer
V≈8×6×3=144 m³, appropriately reported as about 1.4×10² m³ given the rough dimensions.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §2.1.2(a); §2.1.2(b); §2.1.2(c); §2.1.2(d); §2.1.2(e); §2.1.2(f)
Open revision guidance
What to know
- Use base SI quantities kg, m, s, A, K and mol; derive units from definitions (N=kg m s⁻², J=kg m² s⁻², Pa=kg m⁻¹ s⁻², C=A s). Know all units named in the course.
- Use prefixes p, n, μ, m, c, d, k, M, G and T with powers of ten; test dimensional homogeneity by replacing each quantity with base dimensions. Label a graph as quantity/unit, for example speed / m s⁻¹.
What to do in an assessment
- Convert before substitution: 3.0 cm=3.0×10⁻² m and 2.0 cm³=2.0×10⁻⁶ m³. For ρ=m/V, kg/m³ follows from kg divided by m³.
- Check both sides of an equation have the same dimensions; a mismatch such as adding metres to seconds signals an error before arithmetic.
In plain language
SI units expose scale and catch equations that cannot be physically consistent.
Self-check
What SI unit and dimensions follow for pressure p=F/A?
Show the answer
Pa=N m⁻²=kg m⁻¹ s⁻².
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §2.2.1(a); §2.2.1(b); §2.2.1(c); §2.2.1(d)
Open revision guidance
What to know
- A zero/calibration bias is systematic; changing readings are random. Accuracy is closeness to a valid value, precision is repeatability. Absolute uncertainty retains the unit and percentage uncertainty normalises by the measurement.
- For a sum/difference add absolute uncertainties; for product/quotient add fractional (or percentage) uncertainties; for xⁿ multiply percentage uncertainty by |n|. Plot error bars, best-fit and worst acceptable lines, then calculate absolute/percentage difference; only elementary error-bar treatment is required.
What to do in an assessment
- For L=12.0±0.2 cm and W=5.0±0.1 cm, ΔA/A≈0.2/12.0+0.1/5.0=0.0367, so A=60.0 cm²±3.7%.
- If a candidate and reference agree within their stated uncertainty, say consistent within uncertainty; do not infer a statistically precise probability. On a graph, the worst-line gradient spread provides an uncertainty estimate.
In plain language
Uncertainty shows which digits and conclusions the evidence can support.
Self-check
For V=IR, I=2.00±0.02 A and R=10.0±0.2 Ω. Estimate the percentage uncertainty in V.
Show the answer
I contributes 1.0% and R contributes 2.0%; for the product the estimated percentage uncertainty is 3.0%.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §2.3.1(a); §2.3.1(b); §2.3.1(c); §2.3.1(d)
Open revision guidance
What to know
- Scalars such as mass and energy have magnitude; displacement, velocity, force and momentum have magnitude and direction. Vector subtraction adds the reversed vector.
- For two coplanar vectors draw a head-to-tail triangle or resolve perpendicular axes. With angle θ from x: Fx=Fcosθ, Fy=Fsinθ; resultant components add algebraically, R=√(Rx²+Ry²), direction=atan2(Ry,Rx).
What to do in an assessment
- Choose axes and sign convention before resolving; calculate each component, add components separately, then calculate resultant magnitude and quadrant-correct direction.
- For two forces, scale drawing is a check, not a replacement for labels/units and a component calculation when precision matters.
In plain language
Components let vectors be combined by ordinary signed arithmetic.
Self-check
Resolve 10 N at 30° above horizontal.
Show the answer
Fx=10cos30°=8.66 N; Fy=10sin30°=5.00 N.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.1.1(a); §3.1.1(b); §3.1.1(c); §3.1.1(d)
Open revision guidance
What to know
- Displacement is directed change of position; instantaneous speed/velocity are local rates, average speed is total distance/time and average velocity is displacement/time; acceleration is change in velocity/time.
- A displacement–time gradient gives velocity; a velocity–time gradient gives acceleration and signed area gives displacement. Speed–time area gives distance. Tangents distinguish instantaneous from average slope; estimate curved areas with sensible strips.
What to do in an assessment
- From a displacement curve draw a tangent at the requested time, select points on the tangent and calculate Δs/Δt with units. For velocity–time data calculate gradient over a specified interval and add positive/negative areas separately.
- On a speed–time graph add all area magnitudes; on a velocity graph retain signs, then compare distance with displacement.
In plain language
Graphs turn motion history into gradients and areas with physical meanings.
Self-check
Velocity is +3 m s⁻¹ for 4 s then −3 m s⁻¹ for 4 s. Find displacement and distance.
Show the answer
Signed areas cancel, so displacement=0 m; distance=12+12=24 m.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.1.2(a)(i); §3.1.2(a)(ii); §3.1.2(b)(i); §3.1.2(b)(ii); §3.1.2(c)
Open revision guidance
What to know
- For constant acceleration use v=u+at, s=(u+v)t/2, s=ut+½at² and v²=u²+2as, including ideal free fall in uniform g without drag. Define positive direction and check each equation’s assumptions.
- Determine g experimentally using trapdoor/electromagnet release with light-gate/timer methods; investigate motion/collisions with trolley, air track, ticker timer, light gates, data logger or video. Reaction time sets thinking distance; braking distance is separate and stopping distance is their sum.
What to do in an assessment
- Choose the equation omitting the unknown; e.g. from rest over h, v²=2gh, so g=v²/(2h). Repeat release/height/timing, estimate uncertainty and test drag/alignment.
- Calculate thinking distance d=vt_reaction and model braking with work/constant deceleration separately; compare how speed, road and tyre conditions affect the total stopping distance.
In plain language
Free-fall equations are a no-drag model; vehicle stopping combines a reaction phase and a braking phase.
Self-check
A car travels at 20 m s⁻¹ and reaction time is 0.70 s. What is thinking distance?
Show the answer
d=vt=20×0.70=14 m; this excludes braking distance.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.1.3(a); §3.1.3(b)
Open revision guidance
What to know
- Horizontal and vertical motions are independent components sharing the same time. For ideal flight, horizontal acceleration is zero while vertical acceleration is −g; air resistance changes that model.
- Resolve launch velocity into ux=u cosθ and uy=u sinθ. Apply constant-acceleration equations vertically to find time/height, then horizontal x=ux t; a horizontal launch starts with uy=0.
What to do in an assessment
- For a horizontal launch from height h, solve h=½gt² for flight time and multiply by horizontal speed to find range. For an angled launch, check both components against the same elapsed time.
- State where drag matters, particularly for light/slow objects or long flight, and do not mix horizontal and vertical signs.
In plain language
Separate axes simplify a single curved path without giving them different clocks.
Self-check
A ball leaves a table horizontally at 12 m s⁻¹ from 0.80 m high. Estimate its range, neglecting drag.
Show the answer
t=√(2h/g)=√(1.60/9.81)=0.404 s; x=12×0.404=4.85 m.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.2.1(a); §3.2.1(b); §3.2.1(c); §3.2.1(d); §3.2.1(e); §3.2.1(f)
Open revision guidance
What to know
- The resultant force F=ma is recalled; the newton is kg m s⁻². Weight W=mg acts toward Earth’s centre. Tension, normal contact force, upthrust and friction have distinct contact/interacting causes.
- A free-body diagram shows only forces on one chosen body. Sum signed forces in one/two dimensions; constant resultant force gives constant acceleration, while equilibrium needs zero resultant.
What to do in an assessment
- Draw and label every external force, choose axes and write ΣF=ma for each axis; use a consistent sign and separate weight from mass.
- For a 3 kg body with 20 N pull and 5 N opposing friction, a=(20−5)/3=5.0 m s⁻²; include vertical normal/weight if needed.
In plain language
Acceleration follows the vector sum of forces, not one force selected from the diagram.
Self-check
A 2.0 kg body accelerates at 3.0 m s⁻² while a 10 N friction force opposes it. Find the applied pull.
Show the answer
Resultant=ma=6.0 N forward, so pull−10=6 and applied pull=16 N.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.2.2(a); §3.2.2(b); §3.2.2(c); §3.2.2(d)(i); §3.2.2(d)(ii)
Open revision guidance
What to know
- Drag is fluid friction opposing relative motion; it depends on speed, shape, frontal area, surface and fluid properties. A falling body’s weight stays approximately mg, while drag grows and can balance it.
- At terminal speed resultant force and acceleration are zero. PAG1 investigations can use a ball-bearing in viscous liquid or falling cones; vary one factor and record speed versus time.
What to do in an assessment
- For a falling body draw weight down and drag/upthrust up; calculate drag from force balance only when acceleration is zero and buoyancy is included if significant.
- Release identical cones or a bearing through marked positions, time repeated intervals or video-track them, plot speed/time and identify the plateau; control fluid/shape and explain timing/range limits.
In plain language
Terminal velocity is a steady speed because forces balance, not because the body stops.
Self-check
A 2.0 kg object falls at terminal speed with negligible upthrust. Find the drag.
Show the answer
Drag=mg=2.0×9.81=19.6 N upward.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.2.3(a); §3.2.3(b); §3.2.3(c); §3.2.3(d); §3.2.3(e); §3.2.3(f)
Open revision guidance
What to know
- Moment about a pivot is force×perpendicular distance; a couple is equal opposite forces separated by perpendicular distance d, with torque Fd. For static rotational equilibrium clockwise and anticlockwise moments balance.
- Centre of mass is the weighted position of mass; centre of gravity is the resultant weight location in a uniform field. Force equilibrium requires zero vector resultant; three coplanar forces can be shown head-to-tail as a closed triangle.
What to do in an assessment
- Choose a pivot, measure perpendicular lever arms and sum signed moments; for an unknown force equate clockwise and anticlockwise sums. Locate an irregular lamina’s centre of gravity by suspension from two points and crossing plumb lines.
- Draw a scale/vector triangle or resolve three forces into components; check both ΣFx=0, ΣFy=0 and Στ=0 for rigid equilibrium.
In plain language
An object is in equilibrium only when it neither translates nor turns.
Self-check
A 20 N force acts 0.30 m from a pivot. What opposing force at 0.50 m balances its moment?
Show the answer
20×0.30=F×0.50, so F=12 N.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.2.4(a); §3.2.4(b); §3.2.4(c)
Open revision guidance
What to know
- Density ρ=m/V. Pressure p=F/A for solids and p=ρgh for a liquid column (ρgh is the source equation); pressure is force per area. Pressure differences in a fluid give an upthrust.
- Archimedes’ principle states upthrust equals the weight of displaced fluid. Check units: kg m⁻³, Pa and N; use pressure/area forces on opposite faces to explain buoyancy.
What to do in an assessment
- Measure mass and volume, use consistent volume units and calculate ρ. For a submerged body compare bottom/top pressure forces or find weight of displaced fluid.
- A liquid column 0.80 m deep with ρ=1000 kg m⁻³ gives gauge p=ρgh; state that atmospheric pressure is added only if absolute pressure is wanted.
In plain language
Fluids push harder at greater depth, so the pressure difference supports a buoyant force.
Self-check
Calculate gauge pressure 0.80 m below fresh water, taking ρ=1000 kg m⁻³ and g=9.81 m s⁻².
Show the answer
p=ρgh=1000×9.81×0.80=7.85×10³ Pa.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.3.1(a); §3.3.1(b); §3.3.1(c); §3.3.1(d); §3.3.1(e)
Open revision guidance
What to know
- Work is energy transferred by a force; its unit is joule. For force F through displacement x at angle θ, W=Fxcosθ. Energy may be kinetic, gravitational, elastic, thermal, chemical or other stores.
- Energy is conserved in a closed accounting: identify system, stores, transfers and dissipation. The energy transferred by work equals work done; distinguish transfer from energy stored.
What to do in an assessment
- Choose a system boundary, draw an energy pathway and calculate component work with the displacement direction. Sum input and output stores, and state where less-useful thermal/sound transfer goes.
- For a 40 N pull through 3 m at 60°, W=40×3×cos60°=60 J; the force perpendicular to motion does zero work.
In plain language
Energy accounting follows transfer between stores; work measures the mechanical transfer.
Self-check
A 40 N force moves a box 3.0 m at 60° to the displacement. Find work done by that force.
Show the answer
W=Fxcosθ=40×3.0×0.5=60 J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.3.2(a); §3.3.2(b); §3.3.2(c)
Open revision guidance
What to know
- For constant resultant force parallel to displacement, work W=Fs and F=ma give W=mas. From v²−u²=2as, substitute as=(v²−u²)/2 to obtain W=½m(v²−u²)=½mv²−½mu²=ΔEk. Thus Ek=½mv² (taking zero kinetic energy at rest) follows from the work–energy change, rather than being an unrelated formula to memorise. Gravitational potential energy near Earth is Ep=mgh, with a stated datum for h.
- When drag is negligible, falling converts gravitational potential energy into kinetic energy; with resistance, lost mechanical energy transfers mainly to thermal/internal energy.
What to do in an assessment
- To derive the kinetic-energy equation, start with the work done by the resultant force: W=Fs=mas. Replace as using v²−u²=2as, giving W=½m(v²−u²). For an object starting from rest, u=0 and the work transferred to kinetic energy is ½mv².
- For a body dropping through height h from rest, equate mgh=½mv² and cancel mass to obtain v=√(2gh); include efficiency/dissipation if the system is not ideal.
- Calculate kinetic energy from speed not velocity sign, and define the gravitational reference level before comparing Ep.
In plain language
Speed squared controls kinetic energy, while height sets near-Earth gravitational energy.
Self-check
A 2.0 kg object speeds up from 3.0 m s⁻¹ to 7.0 m s⁻¹. Use the work derivation to find its kinetic-energy increase.
Show the answer
W=ΔEk=½m(v²−u²)=½×2.0×(7.0²−3.0²)=40 J. From rest, the same result reduces to Ek=½mv².
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.3.3(a); §3.3.3(b); §3.3.3(c)
Open revision guidance
What to know
- Power is work/energy transferred per time, P=W/t, unit watt. At steady speed in the force direction P=Fv; derive by substituting W=Fx and v=x/t.
- Efficiency=(useful output energy/total input energy)×100%. It cannot exceed 100% for a real energy-conserving process; energy not counted as useful is dissipated or transferred elsewhere.
What to do in an assessment
- Calculate energy or work first, divide by elapsed time for mean power; use instantaneous P=Fv only with the force component parallel to velocity.
- Keep the same energy basis in numerator and denominator and convert both kWh and J consistently; 1 kWh=3.6×10⁶ J.
In plain language
Power tells how quickly energy moves; efficiency tells what fraction serves the intended output.
Self-check
A motor lifts 20 kg through 3.0 m in 5.0 s. Find useful power.
Show the answer
P=mgh/t=20×9.81×3.0/5.0=118 W.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.4.1(a); §3.4.1(b); §3.4.1(c); §3.4.1(d)(i); §3.4.1(d)(ii)
Open revision guidance
What to know
- Tensile loading extends and compressive loading shortens; extension is final minus original length. Hooke’s law gives F=kx in the linear elastic range; k is force per extension in N m⁻¹.
- Measure force–extension (or compression) for springs, wire, rubber band or polythene strip. The graph slope is k only over the linear region and after zero-length/zero-load offsets are handled.
What to do in an assessment
- Clamp the sample consistently, add measured loads in increments, read the extension from a set reference and unload to test reversibility. Repeat and plot F against x with uncertainty.
- Use the fitted linear gradient k=ΔF/Δx; identify the limit where proportionality fails and avoid overloading a sample.
In plain language
A spring constant is the force needed per unit extension only while the relation remains Hookean.
Self-check
A spring extends 4.0 cm under 2.0 N in its linear range. Find k.
Show the answer
k=F/x=2.0/0.040=50 N m⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.4.2(a); §3.4.2(b); §3.4.2(c); §3.4.2(d)(i); §3.4.2(d)(ii); §3.4.2(e); §3.4.2(f)
Open revision guidance
What to know
- Work on a force–extension graph is the area beneath it; for a linear spring elastic energy E=½Fx=½kx². Tensile stress=F/A, strain=ΔL/L, ultimate tensile strength is the maximum stress before failure; Young modulus E=stress/strain.
- Young modulus can be determined for metal by force and extension plus original length and area. Ductile materials show large plastic extension, brittle materials fracture with little plastic strain; polymers show distinct non-linear response. Distinguish elastic recovery from permanent plastic deformation.
What to do in an assessment
- Use a micrometer to measure wire diameter at multiple orientations/positions, calculate A=πd²/4, measure L, load incrementally and determine gradient ΔF/ΔL. Then E=(L/A)(ΔF/ΔL); include uncertainty in d because area depends on d².
- Find work/energy from graph area using trapezia; label elastic, yield/plastic and ultimate points on stress–strain curves and compare shape rather than just gradient.
In plain language
A stress–strain graph separates stiffness, strength and how much permanent deformation remains.
Self-check
A 2.0 m wire, area 1.0×10⁻⁶ m², extends 1.0 mm under 100 N. Find Young modulus.
Show the answer
Stress=100/10⁻⁶=1.0×10⁸ Pa; strain=0.001/2.0=5.0×10⁻⁴; E=2.0×10¹¹ Pa.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.5.1(a); §3.5.1(b); §3.5.1(c); §3.5.1(d); §3.5.1(e)
Open revision guidance
What to know
- Newton’s first law links zero resultant force to unchanged velocity; second law in general is F=Δp/Δt, with F=ma as constant-mass special case; third-law forces are equal/opposite on different bodies. Momentum p=mv is a vector.
- Impulse FΔt=Δp and equals signed area under a force–time graph. For a curved graph estimate area by strips/trapezia; longer collision time for the same Δp reduces average force.
What to do in an assessment
- Choose the interacting object, signed velocity and time interval; calculate p before/after and use Δp/Δt or the area under F–t data. Distinguish action–reaction forces by the body each acts on.
- For a 0.20 kg ball changing velocity from +10 to −5 m s⁻¹, Δp=0.20(−15)=−3.0 N s; report the impulse direction.
In plain language
Momentum includes direction; impulse describes the force effect accumulated over a time.
Self-check
A 0.20 kg ball changes velocity from +10 to −5 m s⁻¹. Find the impulse.
Show the answer
Δp=m(v−u)=0.20(−5−10)=−3.0 N s.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §3.5.2(a); §3.5.2(b); §3.5.2(c)
Open revision guidance
What to know
- For an isolated system total momentum is conserved in each direction. One-dimensional collisions use signed speeds; A-level questions may use two-dimensional vector components.
- Perfectly elastic collisions conserve both total momentum and total kinetic energy; inelastic collisions conserve momentum but reduce kinetic energy of translational motion, often converting it to deformation, sound or thermal energy.
What to do in an assessment
- Draw before/after velocities, choose x/y axes and write momentum conservation separately in each direction; solve unknown final components. Then compare kinetic energies to classify the collision.
- For a perfectly inelastic capture, bodies share one final velocity; for an elastic event, add kinetic-energy equality as a second independent equation.
In plain language
Collision type determines whether kinetic energy remains in translational motion, but momentum remains conserved for an isolated system.
Self-check
A 0.20 kg trolley at 3.0 m s⁻¹ couples to a stationary 0.40 kg trolley. Find their common speed.
Show the answer
0.20×3.0=(0.20+0.40)v; v=1.0 m s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.1.1(a); §4.1.1(b); §4.1.1(c); §4.1.1(d); §4.1.1(e); §4.1.1(f); §4.1.1(g)
Open revision guidance
What to know
- Current is charge flow per time I=ΔQ/Δt; coulomb is ampere-second. Elementary charge magnitude e=1.60×10⁻¹⁹ C, with electron −e and proton +e; net charge is quantised in integer multiples of e.
- In metals current is electron drift, in electrolytes it is ion motion. Conventional current points as positive-charge flow, opposite electron flow. Kirchhoff’s first law follows charge conservation at a junction.
What to do in an assessment
- Calculate Q=It and carrier number N=|Q|/e, stating sign separately. At a junction choose currents consistently and set total current in equal to total out.
- In a metal wire electron drift is opposite the conventional current arrow; do not change current direction conventions in circuit equations.
In plain language
Current counts charge transfer per second, not the speed of one electron.
Self-check
A 0.40 A current flows for 30 s. How many elementary charges pass a cross-section?
Show the answer
Q=It=12 C; N=12/(1.60×10⁻¹⁹)=7.5×10¹⁹ charges.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.1.2(a); §4.1.2(b); §4.1.2(c)
Open revision guidance
What to know
- Mean drift velocity is the average directed speed of mobile charge carriers through a conductor, not their random thermal speed. I=Anev links current to cross-section A, number density n, charge magnitude e and drift speed v.
- Conductors have abundant mobile carriers; semiconductors have intermediate, controllable carrier density; insulators have very few mobile carriers. The distinction in this outcome is in n.
What to do in an assessment
- Rearrange v=I/(Ane), convert A and n to SI, and check that the result has units m s⁻¹. Compare carrier densities before comparing conductivity.
- For a wire, maintain the same current while changing cross-section: lower A requires greater drift speed if n stays fixed.
In plain language
A small directed drift can carry a large current because an enormous number of carriers move through each section.
Self-check
A wire carries 2.0 A; n=8.0×10²⁸ m⁻³ and A=1.0×10⁻⁶ m². Estimate electron drift speed.
Show the answer
v=I/(Ane)=2.0/(1.0×10⁻⁶×8.0×10²⁸×1.60×10⁻¹⁹)=1.56×10⁻⁴ m s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.2.1(a); §4.2.1(b)
Open revision guidance
What to know
- Recognise and draw the ASE standard circuit symbols for cells/batteries, DC supply, switch, resistor, variable resistor, lamp, diode, LED, thermistor, LDR, capacitor, ammeter and voltmeter.
- A circuit diagram represents connectivity rather than physical layout; crossing wires join only when the drawing indicates a junction. Correct polarity is essential for cells, meters, LEDs and other polarised components.
What to do in an assessment
- Redraw a verbal circuit as a labelled symbol diagram, show junctions and polarity, then trace the closed current path. Add ammeters in series and voltmeters in parallel.
- Before powering the circuit, compare the diagram against actual lead connections and component orientation.
In plain language
Circuit symbols make the electrical connections unambiguous.
Self-check
Where are an ammeter and a voltmeter placed when measuring current through and potential difference across a resistor?
Show the answer
The ammeter is in series with the resistor; the voltmeter is connected in parallel across it.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.2.2(a); §4.2.2(b); §4.2.2(c); §4.2.2(d); §4.2.2(e)
Open revision guidance
What to know
- Potential difference is energy transferred per unit charge between two points; the unit volt is J C⁻¹. E.m.f. is energy supplied per charge by a source. Terminal p.d. can be less than e.m.f. when the source has internal resistance or energy is transferred inside it.
- For charge Q, energy transfer W=VQ across a component or W=EQ from source e.m.f. A particle accelerated through potential V gains kinetic energy eV; 1 eV=1.60×10⁻¹⁹ J, so eV=½mv² for a particle starting from rest.
What to do in an assessment
- Track the same charge through a loop and account for source energy supplied and component energy transferred; use a joule-per-coulomb interpretation to avoid confusing e.m.f. with force.
- Convert eV to joules before using SI kinetic-energy equations; for an electron through 100 V, energy gain=100 eV=1.60×10⁻¹⁷ J.
In plain language
A source gives energy to each coulomb; a component transfers that energy elsewhere.
Self-check
An electron starts from rest and crosses 100 V. Estimate its final speed.
Show the answer
½mv²=100e=1.60×10⁻¹⁷ J, so v=√(2E/mₑ)=5.93×10⁶ m s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.2.3(a); §4.2.3(b); §4.2.3(c)(i); §4.2.3(c)(ii); §4.2.3(d)
Open revision guidance
What to know
- Resistance R=V/I in ohms; an ohmic conductor at constant physical conditions has a straight I–V graph through the origin. A filament lamp’s increasing temperature raises resistance, a thermistor is temperature dependent, a diode is directional, and an LED emits light above forward threshold.
- PAG3 investigation compares I–V characteristics for ohmic/non-ohmic components. An LDR’s resistance falls as illumination increases. Record polarity and temperature/light conditions because they change curves.
What to do in an assessment
- Construct a safe series current meter and parallel voltmeter circuit with current limiting, reverse diode polarity, vary the supply in steps, and record paired V,I with uncertainties.
- Plot I against V consistently, identify linear/nonlinear regions and gradients; for an LDR compare resistance at controlled light levels rather than inferring it from brightness alone.
In plain language
A component’s I–V curve reveals whether resistance stays fixed and how it responds to conditions.
Self-check
A resistor has 6.0 V across it and current 0.20 A. Find resistance; state how a filament lamp differs.
Show the answer
R=V/I=30 Ω. A lamp’s filament heats as current rises, so its resistance increases and the I–V graph curves.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.2.4(a)(i); §4.2.4(a)(ii); §4.2.4(b); §4.2.4(c)
Open revision guidance
What to know
- For a uniform wire R=ρL/A, so ρ=RA/L. Resistivity is a material property, unlike resistance which also depends on geometry. PAG3 uses measured metal-wire resistance and dimensions.
- Metal resistivity generally increases with temperature as lattice scattering grows; semiconductor resistivity tends to decrease as carrier density increases. An NTC thermistor therefore has decreasing resistance as temperature rises.
What to do in an assessment
- Measure L, diameter at multiple positions/orientations with micrometer, calculate A=πd²/4, measure V/I, then find ρ=RA/L; propagate diameter uncertainty through A∝d².
- Plot resistance against temperature for an NTC sensor, maintain thermal equilibrium, and use calibration data instead of assuming a linear relationship.
In plain language
Resistivity separates a material’s response from the wire’s shape.
Self-check
A wire has R=4.0 Ω, L=2.0 m and A=1.0×10⁻⁶ m². Find resistivity.
Show the answer
ρ=RA/L=4.0×1.0×10⁻⁶/2.0=2.0×10⁻⁶ Ω m.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.2.5(a); §4.2.5(b); §4.2.5(c)
Open revision guidance
What to know
- Electrical power is P=VI=I²R=V²/R. Energy transferred over time is W=VIt; the equations follow from charge flow and Ohm’s law. The kilowatt-hour is energy, not power.
- Cost is energy use in kWh multiplied by tariff; compare appliance power, operating time and useful output, including environmental consequences of generation.
What to do in an assessment
- Choose the form matching known quantities; use SI values to find joules/watts, or kW×hours for kWh. Check voltage/current are for the same operating condition.
- For a 2.0 kW heater used 3.0 h, energy=6.0 kWh; at £0.30/kWh cost=£1.80.
In plain language
A watt is energy per second; a kilowatt-hour is power multiplied by time.
Self-check
A 60 W lamp runs for 5.0 h. How much energy is used in kWh and at £0.30/kWh what does it cost?
Show the answer
E=0.060×5.0=0.30 kWh; cost=0.30×£0.30=£0.09.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.3.1(a); §4.3.1(b); §4.3.1(c); §4.3.1(d); §4.3.1(e); §4.3.1(f)
Open revision guidance
What to know
- Kirchhoff’s second law expresses conservation of energy around a loop; first law expresses charge conservation at junctions. Series resistances add; for parallel resistors 1/R=Σ(1/Rᵢ).
- Reduce networks carefully, then solve branch currents/voltages; more than one e.m.f. source requires consistent loop directions and source polarity, including opposing sources.
What to do in an assessment
- Label every branch current and rise/drop around each loop. Check junction-current sums and loop-voltage sums after solving.
- For 6 Ω and 3 Ω in parallel, R=2 Ω; in series with 4 Ω total is 6 Ω. For multiple sources, signed source rises and drops must sum with resistor drops to zero.
In plain language
Circuit laws conserve charge at nodes and energy around loops.
Self-check
Two 6 Ω resistors are in parallel, then in series with a 4 Ω resistor. Find total resistance.
Show the answer
Parallel equivalent is 3 Ω; total=3+4=7 Ω.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.3.2(a); §4.3.2(b); §4.3.2(c)(i); §4.3.2(c)(ii)
Open revision guidance
What to know
- A source has e.m.f. E and internal resistance r. When current I flows, terminal p.d. V=E−Ir and lost volts=Ir; equivalently E=I(R+r) for external resistance R and E=V+Ir.
- PAG3 investigation varies load and measures voltage/current to determine source internal resistance; use safe low-voltage supplies/cells and protect against short-circuit heating.
What to do in an assessment
- Take near-open-circuit voltage as e.m.f., then connect known loads and record V,I. Plot V against I: intercept estimates E, negative gradient gives r.
- Check with one point using r=(E−V)/I and compare repeated/fit values; do not short a cell to measure large current.
In plain language
A real source loses some voltage inside itself when it supplies current.
Self-check
A 1.50 V cell supplies 0.20 A and terminal voltage is 1.30 V. Find internal resistance.
Show the answer
r=(E−V)/I=(1.50−1.30)/0.20=1.0 Ω.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.3.3(a); §4.3.3(b); §4.3.3(c)(i); §4.3.3(c)(ii)
Open revision guidance
What to know
- A potentiometer is a potential divider; series components share input voltage in proportion to resistance. A variable resistor, LDR or thermistor changes the ratio and hence output.
- For output across R₂, Vout=R₂/(R₁+R₂)Vin; V₁/V₂=R₁/R₂. Output depends on load resistance, so distinguish unloaded ideal divider from loaded circuit.
What to do in an assessment
- Design a sensor divider, identify which resistor is above/below the output node and predict output as sensor resistance changes. Calculate output at both extremes to check range.
- PAG4 uses a DC supply, sensor, fixed resistor, multimeter and safe range; measure Vout against known light/temperature, repeat and plot calibration.
In plain language
The divider converts a resistance change into a measurable voltage change.
Self-check
Vin=6.0 V, R₁=2.0 kΩ and R₂=4.0 kΩ, with output across R₂. Find Vout.
Show the answer
Vout=(4/(2+4))×6.0=4.0 V.
- Core
Open revision guidance
What to know
- Progressive transverse oscillations are perpendicular to travel; longitudinal oscillations are parallel. Define displacement, amplitude, wavelength, period, phase difference, frequency and speed. f=1/T and v=fλ; represent each with labelled spatial or time graphs.
- Reflection, refraction, polarisation and diffraction apply across wave contexts; diffraction is significant when gap size is comparable with wavelength. Only transverse waves polarise. Intensity I=P/A and for a progressive wave I∝amplitude².
What to do in an assessment
- Use an oscilloscope time-base to find period from horizontal divisions and frequency=1/T. Use ripple tank barriers/slits to observe reflection/refraction/diffraction and measure wavelength/speed.
- Rotate a polariser in a microwave/light setup and record intensity against angle; draw a wave graph with amplitude, wavelength and phase offset labelled.
In plain language
Wave graphs show repeating displacement, while speed and intensity require separate measured quantities.
Self-check
An oscilloscope trace shows 3.0 cycles in 12 ms. Find frequency.
Show the answer
T=12 ms/3=4.0 ms; f=1/(4.0×10⁻³)=250 Hz.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.4.2(a); §4.4.2(b); §4.4.2(c); §4.4.2(d)(i); §4.4.2(d)(ii); §4.4.2(e)
Open revision guidance
What to know
- The electromagnetic spectrum runs radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Representative wavelength orders are radio ~10^3 m, microwave ~10^-2 m, infrared ~10^-5 m, visible ~10^-7 m, ultraviolet ~10^-8 m, X-ray ~10^-10 m and gamma ~10^-12 m; band boundaries vary and overlap. All are transverse electromagnetic waves; higher frequency corresponds to shorter wavelength and higher photon energy.
- Plane polarisation uses light filters or microwave metal grilles. Refractive index n=c/v; Snell’s law n₁sin i₁=n₂sin i₂, angles from normal. At a denser-to-less-dense boundary sin C=1/n; above critical incidence total internal reflection occurs.
What to do in an assessment
- Use a ray box and rectangular/semi-circular block; mark normal, incident/refracted rays, measure angles and test n=sin i/sin r. For TIR use the curved face to direct a ray through the centre and vary incidence at the flat face.
- Compare a given spectrum wavelength with these representative powers of ten (allowing for band overlap); convert prefixes before ranking. Distinguish refraction at an interface from the speed change within a medium.
In plain language
Refraction bends a wave because its speed changes; beyond the critical angle it returns by total internal reflection.
Self-check
A material has refractive index 1.50. Calculate its critical angle in air.
Show the answer
sin C=1/1.50, so C=41.8°.
- Core
Open revision guidance
What to know
- At overlap, resultant displacement is the algebraic sum (superposition). Coherent sources have constant phase difference; path difference and phase difference determine constructive/destructive interference. Same-source two-point sound/microwave interference and Young’s visible-light double slit demonstrate this.
- For slit separation a, screen distance D and small angle, fringe spacing x=λD/a (equivalently λ=ax/D) when a≪D. A diffraction grating has maxima where d sinθ=nλ. Young’s double-slit fringes gave classical evidence for the wave nature of light.
What to do in an assessment
- Draw incident wave profiles and add displacements algebraically. Identify constructive maxima at path difference nλ and destructive minima at (n+½)λ, with coherent sources maintaining constant phase difference. Keep slit separation, fringe order and screen geometry labelled.
- Measure several adjacent fringes over length X and divide by the number of spacings to find x; calculate λ=ax/D. For a grating use d sinθ=nλ with order n, not the double-slit spacing formula.
In plain language
Interference encodes wavelength in the spacing of repeated maxima.
Self-check
Light of wavelength 600 nm passes slits 0.30 mm apart onto a screen 2.0 m away. Find fringe spacing.
Show the answer
x=λD/a=(600×10⁻⁹×2.0)/(3.0×10⁻⁴)=4.0×10⁻³ m=4.0 mm.
- Core
Open revision guidance
What to know
- Stationary patterns form from opposing progressive waves; model them with microwaves, a stretched string or air columns. Nodes have zero displacement and antinodes maximum; adjacent nodes/antinodes are λ/2 apart.
- Stationary and progressive waves share frequency/wavelength but not net energy propagation. Open/closed air columns have different boundary conditions; fundamental is first harmonic and higher harmonics fit permitted patterns. PAG5 resonance-tube method measures sound speed.
What to do in an assessment
- Drive a string or air column, map nodes/antinodes, measure node spacing and infer λ=2×spacing; use v=fλ. In a resonance tube use the difference between consecutive resonance lengths to reduce end-correction error.
- For a string fixed at both ends L=nλ/2; for an open pipe L=nλ/2 and a closed pipe L=(2n−1)λ/4 in ideal modes. State which boundary condition applies.
In plain language
Stationary waves store a pattern in place; node spacing reveals half a wavelength.
Self-check
Adjacent nodes on a string are 0.40 m apart at 100 Hz. Find wave speed.
Show the answer
λ=2×0.40=0.80 m; v=fλ=100×0.80=80 m s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.5.1(a); §4.5.1(b); §4.5.1(c); §4.5.1(d); §4.5.1(e)(i); §4.5.1(e)(ii)
Open revision guidance
What to know
- Electromagnetic radiation transfers energy in photons, each quantum E=hf=hc/λ. The electronvolt is an energy unit; convert eV to J using e. For LED threshold, eV≈hc/λ gives an estimate of h, without semiconductor theory.
- Use different LED colours to test photon-energy proportionality to frequency; turn-on voltage is an approximate threshold and uncertainty includes wavelength band, voltage criterion and contact/electrical conditions.
What to do in an assessment
- For a 500 nm photon, calculate E=hc/λ, then divide by e for eV. To estimate h from an LED, graph eV against 1/λ; gradient is hc and h=gradient/c.
- Measure several LED threshold voltages and wavelengths, include repeated voltage readings and fit rather than relying on one colour.
In plain language
Photon energy increases with frequency and decreases with wavelength.
Self-check
Find the energy of a 500 nm photon in joules and electronvolts.
Show the answer
E=hc/λ=3.98×10⁻¹⁹ J; E/e=2.49 eV.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.5.2(a)(i); §4.5.2(a)(ii); §4.5.2(b); §4.5.2(c); §4.5.2(d); §4.5.2(e); §4.5.2(f)
Open revision guidance
What to know
- In the photoelectric effect a photon interacts one-to-one with a surface electron. Demonstrate with UV on a charged gold-leaf electroscope and zinc plate, respecting UV/electrical safety. Each photon’s energy supplies work function φ and maximum electron kinetic energy: hf=φ+KEmax.
- Threshold frequency f₀=φ/h; below it emission does not occur. Above threshold, raising frequency raises KEmax, while increasing intensity raises photon rate and emitted-electron rate, not each electron’s maximum kinetic energy.
What to do in an assessment
- Use a graph of KEmax against f: slope h and frequency intercept f₀; stopping potential satisfies eVstop=KEmax. Control wavelength and intensity separately to test the two predictions.
- For φ=2.0 eV and photon energy 3.0 eV, subtract in consistent units to find KEmax=1.0 eV; do not use intensity in the energy balance.
In plain language
Frequency controls energy per photon; intensity controls the number of photons arriving per second.
Self-check
Light of frequency 8.0×10¹⁴ Hz hits a metal with work function 2.0 eV. Find KEmax in eV.
Show the answer
hf=(6.63×10⁻³⁴)(8.0×10¹⁴)=5.30×10⁻¹⁹ J=3.31 eV; KEmax=3.31−2.0=1.31 eV.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §4.5.3(a); §4.5.3(b); §4.5.3(c)
Open revision guidance
What to know
- Electron diffraction through a thin polycrystalline graphite foil gives rings because electrons scatter from many crystal orientations; diffraction is evidence of particle wave behaviour. Ring geometry relates wavelength to graphite atomic-plane spacing.
- Every particle has de Broglie wavelength λ=h/p; for non-relativistic electrons accelerated from rest through V, eV=½mv² and p=√(2meV), so λ=h/√(2meV).
What to do in an assessment
- Trace ring diameter/geometry to Bragg-type scattering from known graphite spacing and calculate λ; compare its change with accelerating voltage.
- Use p=mv only in the non-relativistic regime specified; convert momentum in kg m s⁻¹ before evaluating h/p.
In plain language
Moving particles have wavelengths that shrink as their momentum increases.
Self-check
What de Broglie wavelength corresponds to electron momentum 2.0×10⁻²⁴ kg m s⁻¹?
Show the answer
λ=h/p=6.63×10⁻³⁴/(2.0×10⁻²⁴)=3.32×10⁻¹⁰ m.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.1.1(a); §5.1.1(b); §5.1.1(c); §5.1.1(d)
Open revision guidance
What to know
- Thermal equilibrium means no net energy transfer between bodies in thermal contact and permits a common temperature. The absolute thermodynamic kelvin scale does not rely on a particular thermometric substance.
- Read Celsius or kelvin correctly and convert T/K=θ/°C+273 (to course precision); a kelvin interval equals a Celsius interval.
What to do in an assessment
- Use a thermometer calibration point or equation only after the system reaches equilibrium; avoid confusing object temperature with heat transferred.
- For absolute-scale reasoning, state the zero reference and keep kelvin for gas equations.
In plain language
Temperature measures thermal state; heat is energy transferred because of a temperature difference.
Self-check
Convert 25 °C to kelvin.
Show the answer
T=25+273=298 K.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.1.2(a); §5.1.2(b); §5.1.2(c); §5.1.2(d); §5.1.2(e); §5.1.2(f); §5.1.2(g)
Open revision guidance
What to know
- In a solid particles are close/ordered and vibrate; in a liquid they remain close but rearrange; in a gas particles are far apart and move randomly. The simple kinetic model explains these patterns. Brownian smoke motion is a visible result of random molecular impacts.
- Internal energy is the random molecular kinetic plus intermolecular potential energy. At 0 K it is minimum; heating normally increases internal energy and temperature, but during phase change energy changes intermolecular potential while temperature stays constant.
What to do in an assessment
- Use a smoke-cell observation to explain irregular motion by unseen air molecules, not by an active force on the smoke particle.
- Draw a heating curve and annotate sloping temperature-change regions and flat phase-change regions; state which energy store changes in each.
In plain language
During a phase change energy can alter particle arrangement without raising temperature.
Self-check
Why does supplied energy not raise temperature while a pure substance melts at constant pressure?
Show the answer
The energy increases molecular potential energy as bonds/spacing change; mean kinetic energy and therefore temperature remain approximately constant.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.1.3(a); §5.1.3(b)(i); §5.1.3(b)(ii); §5.1.3(c); §5.1.3(d)(i); §5.1.3(d)(ii)
Open revision guidance
What to know
- Specific heat capacity c is energy per unit mass per kelvin; E=mcΔT. Specific latent heat L is energy per unit mass during a phase change; E=mL, with fusion and vaporisation treated separately.
- Electrical methods determine c for a metal block/liquid and L for a solid/liquid by supplying measured electrical energy. Power P=VI gives E=VIt, but heat loss, incomplete immersion and mass/temperature reading uncertainty affect the result.
What to do in an assessment
- For c, insulate sample, measure m, V, I and temperature change, then c=VIt/(mΔT); use a lid/stirrer for liquid and insulation/embedded heater for metal.
- For latent heat, record plateau interval with stable phase change and use L=VIt/m; subtract background heat loss where measured and repeat. Mixture method compares gained/lost heat only after accounting for container.
In plain language
A sample’s temperature change measures heat capacity; a phase plateau measures latent energy.
Self-check
A 0.50 kg block receives 12 kJ and warms by 20 K. Find c.
Show the answer
c=E/(mΔT)=12000/(0.50×20)=1200 J kg⁻¹ K⁻¹.
- Core
Open revision guidance
What to know
- Amount n=m/M and N=nN_A; N_A=6.02×10²³ mol⁻¹. Kinetic theory assumes many random rapidly moving molecules, negligible particle volume, negligible interparticle force except during short perfectly elastic collisions. Pressure results from momentum transfer at walls.
- Use pV=nRT and pV=NkT with absolute kelvin temperature; Boyle pV is constant at fixed T,n and p/T at fixed V,n is constant. Kinetic theory gives pV=(1/3)Nm⟨c²⟩. Equating this with pV=NkT yields (1/3)Nm⟨c²⟩=NkT, hence mean translational kinetic energy per molecule ½m⟨c²⟩=3/2kT; c_rms=√⟨c²⟩. With k=R/N_A, internal energy of an ideal gas is translational molecular kinetic energy. Maxwell–Boltzmann speed distributions start at zero, rise to a most-probable speed, then tail toward high speeds; at a fixed particle count higher temperature broadens and lowers the peak and shifts it to higher speeds, increasing mean and rms speeds.
What to do in an assessment
- Test Boyle’s law with trapped gas at controlled temperature, use pressure/volume readings and plot p against 1/V. For gas thermometer absolute-zero estimate, graph temperature against pressure and extrapolate cautiously to p=0.
- Convert Celsius to kelvin, distinguish mean-square speed from rms speed, and derive ½m⟨c²⟩=3/2kT by equating pV=(1/3)Nm⟨c²⟩ with pV=NkT. Label a Maxwell–Boltzmann curve with most-probable, mean and rms speeds; compare curves at two temperatures and explain the increased high-speed tail.
In plain language
Ideal-gas pressure is the wall effect of moving molecules; temperature sets their average kinetic energy.
Self-check
A gas has n=0.20 mol, T=300 K and V=5.0×10⁻³ m³. Find pressure.
Show the answer
p=nRT/V=(0.20×8.31×300)/(5.0×10⁻³)=9.97×10⁴ Pa.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.2.1(a); §5.2.1(b); §5.2.1(c)
Open revision guidance
What to know
- A radian is arc length/radius; a full turn is 2π rad. Period T is time per revolution, frequency f=1/T, and angular speed ω=2π/T=2πf.
- For steady circular motion count revolutions over a measured interval and calculate f; convert angle to radians for ω formulas.
What to do in an assessment
- Use T=total time/number of turns and check f units s⁻¹. For degrees, θ(rad)=θ(deg)π/180 before applying angular equations.
- The direction of velocity changes even when speed is constant; do not treat angular speed as a linear velocity.
In plain language
Angular speed tells how rapidly angle changes; one revolution is 2π radians.
Self-check
A wheel rotates at 3.0 Hz. Find its period and angular speed.
Show the answer
T=1/3=0.333 s; ω=2πf=18.85 rad s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.2.2(a); §5.2.2(b); §5.2.2(c); §5.2.2(d)(i); §5.2.2(d)(ii)
Open revision guidance
What to know
- A resultant force perpendicular to instantaneous velocity continually changes direction and produces circular motion. For constant speed v=ωr, acceleration a=v²/r=ω²r and inward force F=mv²/r=mω²r.
- Centripetal force is not a new interaction; identify gravity, tension, friction or magnetic force as the actual inward resultant. PAG whirling bung uses radius, mass, period and tension/force to test relation.
What to do in an assessment
- Draw the inward acceleration and identify real force(s) supplying it; calculate period from repeated revolutions and use v=2πr/T.
- For a whirling bung vary one quantity at a time, keep radius measured and safe, record repeated periods, and compare mv²/r with the measured tension.
In plain language
Circular motion needs inward resultant force even at constant speed.
Self-check
A 0.20 kg mass moves at 4.0 m s⁻¹ in a 0.50 m circle. Find inward force.
Show the answer
F=mv²/r=0.20×16/0.50=6.4 N.
- Core
Open revision guidance
What to know
- Define displacement, amplitude, period, frequency, angular frequency and phase; ω=2π/T=2πf. SHM requires acceleration proportional to and opposite displacement: a=−ω²x; solutions x=Acosωt or Asinωt.
- Velocity v=±ω√(A²−x²), vmax=ωA. An ideal oscillator is isochronous: period independent of amplitude. Graph x,v,a with quarter-cycle phase relations. PAG10 measures period/frequency for spring or pendulum systems.
What to do in an assessment
- Time many oscillations from a fiducial crossing, divide by count, repeat at several amplitudes and compare periods; account for damping and human timing.
- At x=0, speed is maximum and acceleration zero; at x=±A, speed zero and acceleration points toward equilibrium. Apply these limits to check an equation or graph.
In plain language
In SHM the restoring acceleration always points toward the centre and grows with displacement.
Self-check
A mass has ω=5.0 rad s⁻¹ and amplitude 0.080 m. Find maximum speed and acceleration at the endpoint.
Show the answer
vmax=ωA=0.40 m s⁻¹; |a|max=ω²A=25×0.080=2.0 m s⁻².
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.3.2(a); §5.3.2(b)
Open revision guidance
What to know
- During SHM kinetic and potential energy exchange; total mechanical energy is constant in the ideal undamped oscillator. For a spring E=½kA²; kinetic energy is greatest at equilibrium, elastic potential greatest at endpoints.
- Energy–displacement graphs are non-linear: spring potential ½kx² is parabolic and kinetic energy is total minus that curve.
What to do in an assessment
- Draw total energy as a horizontal line and identify K and U at x=0 and x=±A. Calculate U=½kx² then K=Etotal−U.
- If oscillation is damped, show total mechanical energy falling as transfer to thermal/sound; do not force a constant-total graph onto a damped system.
In plain language
The oscillator trades kinetic and potential energy while total ideal energy stays fixed.
Self-check
A spring oscillator has total energy 0.40 J and potential energy 0.10 J at a point. Find kinetic energy there.
Show the answer
K=Etotal−U=0.30 J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.3.3(a); §5.3.3(b)(i); §5.3.3(b)(ii); §5.3.3(c); §5.3.3(d); §5.3.3(e)
Open revision guidance
What to know
- Free oscillations occur after displacement without continuous drive; forced oscillations respond to a periodic driver. Damping transfers energy away, reducing amplitude; observe this for different systems.
- Resonance is a large response near natural frequency. Amplitude-driving-frequency curves peak near resonance; greater damping lowers/broadens the peak. Practical examples include bridges, buildings, vehicles and musical instruments.
What to do in an assessment
- Measure steady-state amplitude over a range of driving frequencies, keep drive amplitude fixed, and plot amplitude/frequency; wait for transients to settle.
- Compare damping by adding controlled resistance/friction and explain why useful or harmful resonance depends on context, risk and design.
In plain language
Driving near a system’s natural frequency can produce a large oscillation.
Self-check
A driven oscillator has natural frequency 4.0 Hz. At what drive frequency is its amplitude expected to peak most strongly when damping is small?
Show the answer
Near 4.0 Hz (the resonant frequency); damping and system coupling determine the peak height and exact position.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.4.1(a); §5.4.1(b); §5.4.1(c); §5.4.1(d); §5.4.1(e)
Open revision guidance
What to know
- Mass creates a gravitational field; outside a spherically symmetric body, model its mass as a point at its centre. Field lines map direction and relative strength; they point toward mass.
- Field strength g=F/m is force per unit test mass, N kg⁻¹ (=m s⁻²); gravitational fields are one field type that exerts forces at a distance.
What to do in an assessment
- Draw radial lines with arrows inward and closer spacing where field stronger; around a spherical body use centre-to-centre distance.
- Use g=W/m for a small test mass and compare with near-Earth g only where its field is approximately uniform.
In plain language
A field describes the force a mass would experience at each position.
Self-check
A 2.0 kg test mass experiences 19.6 N weight. Find field strength.
Show the answer
g=F/m=19.6/2.0=9.8 N kg⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.4.2(a); §5.4.2(b); §5.4.2(c)
Open revision guidance
What to know
- For point masses F=GMm/r² (attractive) and a point mass M produces g=GM/r². Use centre-to-centre separation and N m² kg⁻² for G.
- Close to Earth’s surface g is approximately uniform and numerically equal to free-fall acceleration; this local approximation differs from inverse-square change over large altitude.
What to do in an assessment
- Substitute both masses and centre separation; verify inverse-square behaviour by doubling r, which quarters F and g.
- For near-surface weight use W=mg; do not insert Earth radius in this local equation unless calculating from Earth’s mass.
In plain language
Gravity weakens with the square of distance from the source centre.
Self-check
If separation between two masses triples, what fraction of their original gravitational force remains?
Show the answer
F∝1/r², so Fnew/Fold=1/3²=1/9.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.4.3(a); §5.4.3(b); §5.4.3(c); §5.4.3(d); §5.4.3(e)
Open revision guidance
What to know
- Kepler’s laws: elliptical orbits with Sun at one focus; equal areas in equal times; T²∝r³. For circular orbit, gravity provides centripetal force, giving T²=4π²r³/(GM).
- Kepler’s third-law proportionality applies to other systems orbiting the same central mass. A geostationary satellite has a 24 h equatorial prograde orbit and appears fixed above one longitude; it supports communications/weather applications.
What to do in an assessment
- Set GMm/r²=mv²/r, substitute v=2πr/T and derive T²=4π²r³/(GM). Cancel m and preserve SI units.
- Find geostationary radius from the period and Earth GM; discuss coverage, expense and collision/debris risks rather than assuming such orbit is over any latitude.
In plain language
Orbit period increases with orbital radius; the central body sets the proportionality.
Self-check
For an Earth satellite with T=24 h, what special apparent motion defines geostationary orbit?
Show the answer
It travels prograde in the equatorial plane with the same period as Earth’s rotation, so it remains above one longitude.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.4.4(a); §5.4.4(b); §5.4.4(c); §5.4.4(d); §5.4.4(e)
Open revision guidance
What to know
- Gravitational potential Vg is work done per unit mass bringing a test mass from infinity; zero is defined at infinity. For point mass M, Vg=−GM/r, and change is final minus initial potential.
- Work equals area under force–distance graph (with path/sign convention); gravitational potential energy Ep=mVg=−GMm/r. Escape speed is the minimum launch speed to reach infinity with zero final kinetic energy.
What to do in an assessment
- Plot attractive force magnitude against r and integrate/estimate area for work; use potential difference for energy changes. For escape, ½mv²−GMm/r=0, so vesc=√(2GM/r).
- State negative potential relative to infinity and use a positive energy requirement for escape; compare with planet atmosphere particle speeds only as a thermal model.
In plain language
A bound object has negative gravitational potential energy relative to infinity.
Self-check
Find escape speed from a planet with GM=4.0×10¹⁴ m³ s⁻² and radius 2.0×10⁶ m.
Show the answer
vesc=√(2GM/r)=√(4.0×10⁸)=2.0×10⁴ m s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §5.5.1(a); §5.5.1(b); §5.5.1(c); §5.5.1(d); §5.5.1(e); §5.5.1(f); §5.5.1(g)
Open revision guidance
What to know
- Distinguish planet, planetary satellite, comet, solar system, galaxy and universe. A star forms when interstellar dust/gas undergoes gravitational collapse; core hydrogen fuses to helium and radiation plus gas pressure oppose further collapse.
- A low-mass Sun-like star becomes a red giant, sheds a planetary nebula and leaves a compact, hot white dwarf supported by electron degeneracy below the Chandrasekhar limit. A massive star becomes a red supergiant then supernova, leaving an ultra-dense neutron star or a black hole whose gravity prevents escape from within its event horizon. The HR diagram plots luminosity against surface temperature and locates main sequence, red giants, super red giants and white dwarfs.
What to do in an assessment
- Read an HR diagram using its temperature-axis direction and luminosity; identify locations and likely evolutionary paths rather than claiming stars move through every region.
- Explain the low-/high-mass branches from fusion fuel and gravitational balance; compare white-dwarf degeneracy, neutron-star compactness and black-hole event-horizon behaviour.
In plain language
Mass determines whether a star ends as a white dwarf or a compact massive remnant.
Self-check
Where does a Sun-like star lie after it sheds a planetary nebula?
Show the answer
It becomes a white dwarf, supported against collapse by electron degeneracy pressure.
- Core
Open revision guidance
What to know
- Isolated gas atoms have discrete electron energy levels, negative relative to zero at ionisation. A photon is emitted in a downward transition with hf=ΔE=hc/λ; absorption lines form when cooler gas removes selected wavelengths from a continuous spectrum, while hot thin gas produces emission lines. Different atoms have characteristic spectral lines for identification.
- A transmission grating obeys d sinθ=nλ. Wien’s displacement law links λmax inversely to stellar surface temperature, and Stefan’s law L=4πR²σT⁴ allows radius to be inferred from luminosity and temperature. The required content uses spectra and the grating relation, not construction/use of an optical spectrometer.
What to do in an assessment
- Distinguish continuous, emission-line and absorption-line spectra; match line patterns to elements and use known grating spacing and maxima angles to calculate wavelength.
- Calculate T from λmax, then R=√(L/(4πσT⁴)); label units and compare the result with plausible stellar scale.
In plain language
A spectrum links specific photon energies to elements and temperature.
Self-check
A star has peak wavelength 500 nm. Estimate its surface temperature using b=2.90×10⁻³ m K.
Show the answer
T=b/λmax=2.90×10⁻³/(5.00×10⁻⁷)=5.80×10³ K.
- Core
Open revision guidance
What to know
- AU, light-year and parsec describe astronomical distances. Stellar parallax p in arcseconds gives d/pc=1/p. The cosmological principle states that the Universe is homogeneous and isotropic on large scales and that the laws of physics are universal.
- For a slowly receding source the electromagnetic Doppler approximation is Δλ/λ≈Δf/f≈v/c; galactic redshift supports an expanding-Universe model and Hubble law v≈H₀d. Express H₀ in km s⁻¹ Mpc⁻¹ or s⁻¹ and convert before using t≈H₀⁻¹. The Big Bang model describes expansion of space-time from an early hot, dense state: the early Universe cooled as it expanded; light nuclei formed, later electrons combined with nuclei and the 2.7 K microwave background decoupled, then gravity gathered matter into stars and galaxies. Expansion continues. Redshift and microwave-background measurements support this history; current composition includes dark energy and dark matter with only a small fraction ordinary matter.
What to do in an assessment
- Calculate parallax distance and convert among AU, ly and pc; infer low-speed recession from fractional wavelength/frequency shift and test Hubble’s relation using galaxy distance/redshift data.
- Convert H₀ to s⁻¹ and estimate age t≈H₀⁻¹, stating this simplified expansion-rate estimate. Trace the model chronology—hot dense expansion, cooling, light-element formation, background radiation/free atoms, gravitational formation of stars and galaxies, and continuing expansion—and distinguish this interpretation from the measured redshift and background evidence.
In plain language
Cosmic expansion is inferred from several independent observations, not one image of a beginning.
Self-check
A star’s parallax is 0.20 arcsec. Find its distance in parsecs.
Show the answer
d=1/p=1/0.20=5.0 pc.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.1.1(a); §6.1.1(b); §6.1.1(c); §6.1.1(d); §6.1.1(e)(i); §6.1.1(e)(ii)
Open revision guidance
What to know
- Capacitance C=Q/V is charge stored per volt, measured in farads. During charging electrons collect on one plate and leave the other through the circuit; no electrons cross the dielectric. Series capacitors obey 1/Ceq=Σ1/Ci; parallel capacitors Ceq=ΣCi.
- Analyse networks containing resistors and capacitors by applying circuit laws and equivalent capacitance. PAG9 combines capacitors in series/parallel with ammeters and voltmeters; discharge through a resistor before changing connections.
What to do in an assessment
- For two 6 μF capacitors in series, 1/Ceq=1/6+1/6 so Ceq=3 μF; in parallel, Ceq=6+6=12 μF. Check that a series equivalent is below either capacitor and a parallel equivalent equals their sum.
- Measure voltage across each capacitor and branch current without placing an ammeter in parallel; compare measured charge Q=CV for the same applied voltage. Series equivalent is below either capacitor; parallel equivalent equals their sum.
In plain language
Capacitors store separated charge; the connection determines total capacitance.
Self-check
Two 6 μF capacitors are connected in series. Find their equivalent capacitance.
Show the answer
1/Ceq=1/6+1/6, so Ceq=3 μF.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.1.2(a); §6.1.2(b); §6.1.2(c)
Open revision guidance
What to know
- For a capacitor graph with potential difference V on the vertical axis and charge Q on the horizontal axis, stored energy W is the area under V(Q): W=∫VdQ. For a linear capacitor W=½QV=Q²/(2C)=½CV². A graph with Q on the vertical axis instead has area ∫QdV and is not the energy expression.
- Capacitors provide stored electrical energy in flash units, smoothing and timing/energy applications; assess charging voltage, stored energy and safe discharge before handling.
What to do in an assessment
- Label axes explicitly: put Q horizontally and V vertically, then calculate the area under the V–Q graph to obtain energy. For a straight line from the origin, use triangle area ½QV and verify it equals ½CV² using Q=CV.
- Calculate W using whichever of Q,V,C is known, then compare with any stated device energy demand; never treat stored charge as an ideal unlimited source.
In plain language
The area under voltage versus charge is stored energy.
Self-check
A 100 μF capacitor is charged to 12 V. Find its stored energy.
Show the answer
W=½CV²=0.5×100×10⁻⁶×144=7.2×10⁻³ J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.1.3(a)(i); §6.1.3(a)(ii); §6.1.3(b); §6.1.3(c); §6.1.3(d); §6.1.3(e)
Open revision guidance
What to know
- For an RC circuit τ=RC. Discharging voltage/current/charge follows x=x₀e^(−t/RC); charging approaches its final value x=x₀(1−e^(−t/RC)). For discharge dq/dt=−q/RC. After one τ, discharge falls to 1/e and charge reaches 1−1/e of final.
- PAG9 uses meters/data logger to record charge/discharge. ln x against t is linear for discharge with gradient −1/RC; exponential graphs have a constant ratio over equal time intervals. Spreadsheet modelling connects differential rate form, curve and log plot.
What to do in an assessment
- Build a low-voltage series RC circuit, record V or I at known times with repeated readings, determine τ from 63%/37% points or ln graph, and compare with RC. Discharge before reconfiguration.
- For spreadsheet, calculate predicted x=x₀e^(−t/RC), graph model and data; inspect residuals and time resolution, then vary R or C one at a time.
In plain language
The resistor controls how quickly the capacitor’s stored charge changes.
Self-check
A 47 μF capacitor is connected to a 100 kΩ resistor. Find τ and the discharge fraction after one τ.
Show the answer
τ=RC=4.7 s; x/x₀=e⁻¹=0.368.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.2.1(a); §6.2.1(b); §6.2.1(c); §6.2.1(d)
Open revision guidance
What to know
- Electric fields are due to charges. Outside a uniformly charged sphere, model its field as if its charge were concentrated at the centre. Field lines map direction and relative strength; they leave positive and enter negative charge.
- Electric field strength E=F/q is force per positive test charge, N C⁻¹ (=V m⁻¹). Field lines never cross; their density represents field strength.
What to do in an assessment
- Sketch radial fields for isolated point charge and dipole; reverse arrow direction for negative source. Calculate E by dividing force by a small positive test charge.
- Use spherical symmetry only where charge distribution is uniform and observation is outside the sphere; do not treat a non-uniform sphere as a point automatically.
In plain language
A field diagram shows which way a positive test charge would be pushed.
Self-check
A 2.0 μC positive test charge feels 0.040 N. Find field strength.
Show the answer
E=F/q=0.040/(2.0×10⁻⁶)=2.0×10⁴ N C⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.2.2(a); §6.2.2(b); §6.2.2(c); §6.2.2(d)
Open revision guidance
What to know
- For point charges F=Qq/(4πε₀r²), with attraction/opposition determined by signs; point-charge field E=Q/(4πε₀r²) with direction. Both electric and gravitational point fields are inverse-square and central; gravity between masses is attractive, while electric force may attract or repel.
- Fields are models for forces at a distance and should be linked consistently to force, potential and energy; gravitational laws from §5.4 provide the comparison.
What to do in an assessment
- Substitute signed charges and centre separation, calculate magnitude then infer direction from signs. Compare relative force on particles by including their charge or mass.
- At fixed r, electric force on charges scales with Qq; gravitational force scales with Mm. State why gravity dominates astronomical systems despite weaker microscopic interaction.
In plain language
Electric and gravitational fields share geometry but not source sign or force direction.
Self-check
Two charges +2 μC and −3 μC are 0.10 m apart. Find the force magnitude using 1/(4πε₀)=8.99×10⁹.
Show the answer
F=8.99×10⁹(2×10⁻⁶×3×10⁻⁶)/(0.10²)=5.39 N, attractive.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.2.3(a); §6.2.3(b); §6.2.3(c)
Open revision guidance
What to know
- Between parallel plates E=V/d; field lines are uniform away from edges. A plate capacitor C=ε₀A/d, or εA/d with ε=εrε₀; relative permittivity scales capacitance, and the specification does not require why εr≥1.
- A charged particle experiences F=qE and accelerates according to Newton’s law; combine with kinematics, work/energy and earlier motion outcomes.
What to do in an assessment
- Draw the field from positive to negative plate, calculate E using plate separation, then use signed F=qE and a=F/m. Check whether it enters with horizontal or vertical initial velocity.
- Use energy qV=ΔEk for motion across a potential difference; compare with force-time or trajectory method and identify when plate-edge effects invalidate uniform-field approximation.
In plain language
A uniform field pushes positive and negative charges in opposite directions.
Self-check
An electron crosses 200 V from rest. Find its kinetic-energy gain in eV and joules.
Show the answer
ΔEk=200 eV=200×1.60×10⁻¹⁹=3.20×10⁻¹⁷ J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.2.4(a); §6.2.4(b); §6.2.4(c); §6.2.4(d); §6.2.4(e)
Open revision guidance
What to know
- Electric potential V at a point is work per unit positive charge from infinity; define V=0 at infinity. For point charge Q, V=Q/(4πε₀r), and change is final minus initial potential. An isolated sphere has C=4πε₀R, derived from V and Q=CV.
- Force–distance graph area gives work with signs; electric potential energy U=qV=Qq/(4πε₀r) for point charges. Positive/negative sign depends on charge pair and reference.
What to do in an assessment
- Find potential at each point and calculate ΔU=qΔV; derive isolated-sphere C by setting V=Q/(4πε₀R), then C=Q/V.
- For force graph, calculate area and direction convention; compare with potential-energy change to check energy conservation.
In plain language
Potential is energy per coulomb; multiplying by the test charge gives energy.
Self-check
An isolated conducting sphere has radius 0.10 m. Find its capacitance.
Show the answer
C=4πε₀R=4π(8.85×10⁻¹²)(0.10)=1.11×10⁻¹¹ F.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.3.1(a); §6.3.1(b); §6.3.1(c); §6.3.1(d); §6.3.1(e)(i); §6.3.1(e)(ii); §6.3.1(f)
Open revision guidance
What to know
- Magnetic fields arise from moving charge/current or permanent magnets. Draw field lines from N to S outside a magnet; current-carrying straight wire is concentric, a flat coil resembles a bar magnet, and a long solenoid has a strong nearly uniform internal field.
- Fleming’s left-hand rule links conventional current, field and force. A wire experiences F=BILsinθ; flux density B is measured in tesla. PAG practical measures B between pole faces using wire and digital balance.
What to do in an assessment
- Reverse current or field to check force direction. For the balance method measure mass change Δm, then F=Δmg and B=F/(IL) for perpendicular wire; vary current and repeat.
- Keep active wire length within uniform gap, measure current with ammeter and avoid heating/magnet movement; describe uncertainty in Δm, I and L.
In plain language
Magnetic field strength is measured by how much force it gives a current or moving charge.
Self-check
A 0.10 m wire carries 2.0 A perpendicular to a 0.30 T field. Find force.
Show the answer
F=BIL=0.30×2.0×0.10=0.060 N.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.3.2(a); §6.3.2(b); §6.3.2(c)
Open revision guidance
What to know
- At right angles to uniform B, a charge q moving at speed v experiences F=B|q|v. Since force is perpendicular to velocity it bends the path without changing speed; set Bqv=mv²/r to obtain r=mv/(B|q|).
- In crossed electric and magnetic fields a velocity selector passes particles undeflected when electric and magnetic forces balance, E=Bv; otherwise trajectory curves.
What to do in an assessment
- Draw force direction for positive charge, reverse for negative; use circular radius to infer momentum/charge ratio and check field region uniformity.
- For selector calculate v=E/B, identify plate polarity and magnetic orientation, and explain how unwanted speeds deflect.
In plain language
A magnetic force bends a moving charge but does no work when it stays perpendicular to motion.
Self-check
A proton moves at 2.0×10⁶ m s⁻¹ perpendicular to 0.50 T. Find force magnitude.
Show the answer
F=Bqv=0.50×1.60×10⁻¹⁹×2.0×10⁶=1.6×10⁻¹³ N.
- Core
Open revision guidance
What to know
- Magnetic flux through a coil is Φ=BAcosθ in weber, and an N-turn coil has flux linkage NΦ. A search coil connected to a fluxmeter or a voltage sensor/data logger measures a change in flux linkage: induced emf ε=−Δ(NΦ)/Δt, so integrating emf over time gives −Δ(NΦ). A steady flux produces no induced emf; the flux must be changed during the measurement.
- A simple a.c. generator rotates a coil in a magnetic field. As coil area-normal direction changes, flux linkage NΦ=NBAcosθ changes, inducing an emf by Faraday’s law; after each half-turn the emf reverses, giving alternating output. Slip rings and brushes connect the rotating coil to the external circuit. An ideal laminated iron-core transformer has Ns/Np=Vs/Vp=Ip/Is; lamination reduces eddy-current heating.
What to do in an assessment
- Sketch the magnet, rotating coil, axle, slip rings and brushes. Follow the coil through a half-turn to show flux linkage and induced emf changing sign; connect the alternating output to the changing flux linkage, not to a changing field source.
- To investigate flux with a search coil, connect its known turn count to a zeroed fluxmeter, or to a voltage sensor/data logger that records emf against time. Place the coil in the field and deliberately change its orientation from its initial position to a defined final position; record the fluxmeter change or integrate the emf–time trace to obtain Δ(NΦ). Divide by N for ΔΦ, and use Φ=BAcosθ with the coil area and angle to infer B when appropriate. Repeat with controlled changes in angle or field; keep the coil, area and movement protocol fixed when comparing trials, and distinguish a change in total flux from a change in movement speed (which changes the peak emf). A field probe or known-area coil can give an independent comparison.
- Use low-voltage isolated AC for transformer practical, record primary/secondary turns, voltage/current, calculate ratios and power loss; explain grid transmission at high voltage to reduce I²R loss.
In plain language
Induction is caused by changing magnetic flux, and its direction resists that change.
Self-check
A 200-turn search coil is rotated from its plane parallel to a uniform field to its plane perpendicular to the field. Its fluxmeter indicates a change in flux linkage of 0.040 Wb-turn. What is the flux change per turn?
Show the answer
ΔΦ=Δ(NΦ)/N=0.040/200=2.0×10⁻⁴ Wb per turn. The change occurs because the coil’s angle to the field changes; a stationary coil in steady flux would induce no emf.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.4.1(a); §6.4.1(b); §6.4.1(c); §6.4.1(d); §6.4.1(e); §6.4.1(f); §6.4.1(g)
Open revision guidance
What to know
- Rutherford alpha scattering showed most alpha particles pass through but a few deflect strongly, implying a tiny dense positive nucleus in an atom mostly empty space. Nuclei contain protons and neutrons; electrons are also constituents of atoms but are outside the nucleus, not nucleons. A neutral atom has Z electrons to balance the +Ze charge of its Z protons; those electrons do not contribute to nucleon number A. Proton number Z and nucleon number A define isotope notation ᴬ_ZX.
- The atom is about 10^-10 m across and a nucleus about 10^-15 m: a linear size ratio near 10^5 and a volume ratio near 10^15, so the atom is mostly empty space. Strong nuclear force is short-range, attractive to about 3 fm and repulsive below about 0.5 fm. Nuclear radius R=r₀A^(1/3). For order estimates, a typical atomic mean density is ~10^3 kg m⁻³, while nuclear mean density is ~10^17 kg m⁻³.
What to do in an assessment
- Use Rutherford scattering to infer concentrated positive charge; identify Z protons in the nucleus and, for a neutral atom, Z electrons outside it. Count only protons and neutrons in A, so neutron number is A−Z; conserve A and Z for isotope notation. Compare the length and volume scales, then calculate a nuclear mean density ρ≈Am_nucleon/(4πR³/3) and a representative atomic density from mass/atomic volume.
- Estimate mass≈A m_nucleon and density; check how R∝A^(1/3) makes nuclear volume approximately proportional to A, hence density nearly constant.
In plain language
The nucleus is tiny compared with the atom but holds nearly all its mass.
Self-check
For A=125 and r₀=1.2 fm, estimate nuclear radius.
Show the answer
R=1.2×125^(1/3) fm=1.2×5=6.0 fm.
- Core
Open revision guidance
What to know
- Particle/antiparticle pairs include electron–positron, proton–antiproton, neutron–antineutron and neutrino–antineutrino. A particle and its corresponding antiparticle have equal mass; electron/positron and proton/antiproton charges are opposite, while neutron and neutrino are neutral. Hadrons (proton, neutron) experience strong and weak interactions; leptons (electron, neutrino) experience weak but not strong interaction.
- Use u,d,s quarks and antiquarks: u=+2e/3, d=s=−e/3, antiparticle signs reverse; proton uud has +e, neutron udd has 0. β−: d→u+e⁻+anti-ν; β+: u→d+e⁺+ν. Check charge conservation and explain particle decays through quark change.
What to do in an assessment
- Classify before balancing; add constituent quark charges to verify proton/neutron and all antiparticle signs. Write beta transformation at quark and nucleon level and conserve charge, baryon number and lepton number in the stated model.
- For β− neutron decay, udd→uud+e⁻+anti-ν; charges 0=+1−1+0. Identify which d quark transforms and state that weak interaction mediates it.
In plain language
Quarks are constituents of hadrons; lepton and hadron interactions distinguish the families.
Self-check
What quark changes in β− decay, and what is the charge check?
Show the answer
A down quark changes to up: −e/3 becomes +2e/3 while emitting e⁻ (−e); total charge remains −e/3.
- Core
Open revision guidance
What to know
- Radioactive decay is spontaneous and random; probability applies to each nucleus, while large samples show predictable activity A=λN. An α particle is strongly ionising with a short range (typically centimetres in air) and is stopped by paper/thin material; β radiation is less ionising, travels farther and is stopped by a few millimetres of aluminium/plastic; γ is weakly ionising but highly penetrating and is attenuated by thick lead/concrete. Actual penetration depends on radiation energy and absorber; α>β>γ is the typical ionising-power order.
- Balance nuclear equations for α, β−, β+; half-life λt½=ln2. A=A₀e^(−λt), N=N₀e^(−λt), and dN/dt=−λN. Simulated dice model independent chance; carbon dating compares remaining isotope with calibrated initial abundance.
What to do in an assessment
- Measure background, subtract it, keep source-detector geometry fixed and record count rate behind successive absorbers: paper for α, thin aluminium/plastic for β, then increasing lead thickness for γ attenuation. Use a safe sealed source, maximise distance, minimise time, use approved shielding/detector procedure and compare repeat counts because decay is random.
- Record activity versus time, fit lnA against t or identify half-activity, use spreadsheet/dice model, then calculate age t=ln(N₀/N)/λ with uncertainty and calibration limitations.
In plain language
Radioactive decay is unpredictable for one nucleus but follows a statistical exponential for many.
Self-check
A source has half-life 6.0 h. What fraction remains after 18 h?
Show the answer
Three half-lives have passed; fraction=(1/2)³=1/8=0.125.
- Core
Open revision guidance
What to know
- Einstein’s equation ΔE=Δmc² converts mass change to energy; pair creation requires energy at least 2m_ec², and annihilation converts particle/antiparticle mass to photons. Mass defect is separated nucleon mass minus bound-nucleus mass; binding energy per nucleon relates stability.
- Plot binding energy per nucleon against A: release energy when products move toward higher binding energy/nucleon. Calculate nuclear binding from masses. Induced fission can release neutrons and sustain chain reaction; reactor fuel rods, control rods and moderator have distinct roles. Fusion of light nuclei needs high temperature; balance A and Z. Evaluate radioactive waste and power impacts using evidence.
What to do in an assessment
- Convert atomic mass defect to kg or use mass units consistently with c²; calculate total energy change of reactants/products, then divide by nucleon count for binding energy per nucleon.
- Draw chain-reaction sequence, explain control rods absorb neutrons and moderator slows them, and distinguish fuel from control. Balance every nuclear transformation and compare waste, reliability, emissions, accident risk and alternatives without a blanket claim.
In plain language
Nuclear energy comes from changes in binding energy, not from mass disappearing without accounting.
Self-check
A reaction has mass defect 2.0×10⁻²⁹ kg. Estimate energy released.
Show the answer
ΔE=Δmc²=2.0×10⁻²⁹×(3.00×10⁸)²=1.8×10⁻¹² J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.5.1(a); §6.5.1(b); §6.5.1(c); §6.5.1(d); §6.5.1(e); §6.5.1(f); §6.5.1(g)
Open revision guidance
What to know
- An X-ray tube heats a cathode to emit electrons, accelerates them through high voltage to a metal anode/target, and produces X-rays by rapid deceleration and target transitions. Attenuation includes scattering, photoelectric absorption, Compton interaction and pair production at sufficient photon energy.
- Intensity follows I=I₀e^(−μx). Barium/iodine contrast increases absorption in selected anatomy. CAT/CT rotates a thin fan-beam tube around the patient; a detector ring and computer reconstruct/display cross-sections. Compared with a projection X-ray it reduces superposition and localises structures, but adds dose/cost.
What to do in an assessment
- For known μ and thickness x calculate transmitted intensity; plot ln(I/I₀) versus x with gradient −μ. Explain why dense bone/contrast agent appears different from soft tissue.
- Describe source, patient, detector, rotation and reconstruction; compare diagnostic information, radiation dose, availability and risk before recommending CT.
In plain language
Attenuation makes different tissues transmit different amounts of X-ray energy.
Self-check
A tissue path has μ=0.20 mm⁻¹ and thickness 5.0 mm. What fraction of X-ray intensity remains?
Show the answer
I/I₀=e^(−μx)=e⁻¹=0.368.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.5.2(a); §6.5.2(b); §6.5.2(c); §6.5.2(d); §6.5.2(e)
Open revision guidance
What to know
- Technetium-99m and fluorine-18 are tracers. A gamma camera uses a collimator to select direction, scintillator to convert gamma photons to light, photomultiplier tubes to produce electrical pulses, and computer/display to build an image.
- A PET tracer emits positrons; annihilation with electrons creates paired approximately opposite photons detected in coincidence to reconstruct tracer distribution. Gamma-camera/PET images diagnose function; scanner expense/availability and radiation risk create clinical/ethical decisions.
What to do in an assessment
- Trace each event from tracer accumulation through detector signal to image; explain collimator’s direction selection and why coincidence improves PET location.
- Compare which physiological function is imaged, preparation/half-life and dose; weigh diagnostic benefit and alternatives, not just instrument cost.
In plain language
A tracer image shows where a radiopharmaceutical is taken up, not a direct anatomical photograph.
Self-check
Why are coincident opposing photons useful in PET?
Show the answer
They indicate an annihilation along a line joining detectors; many such events reconstruct the tracer distribution.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), §6.5.3(a); §6.5.3(b); §6.5.3(c); §6.5.3(d); §6.5.3(e); §6.5.3(f); §6.5.3(g)
Open revision guidance
What to know
- Ultrasound is a longitudinal wave above 20 kHz. Piezoelectric transducers convert electrical pulses to acoustic waves and returning echoes back to signals. A-scan plots echo amplitude against time; B-scan maps echo positions into an image.
- Acoustic impedance Z=ρc; intensity reflection ratio Ir/I₀=[(Z₂−Z₁)/(Z₂+Z₁)]². Matching gel reduces air/tissue mismatch. Doppler shift determines blood speed: Δf/f=2vcosθ/c for reflection, with angle between beam and flow.
What to do in an assessment
- Calculate echo depth d=ct/2; use pulse timing for A-scan and scan position/echo strength for B-scan. For reflection compare impedances and state why gel improves coupling.
- Measure Doppler shift and beam angle, rearrange v=(Δf/f)c/(2cosθ), use SI units and discuss angle uncertainty and flow-direction assumptions.
In plain language
Ultrasound images use returning echoes, and gel helps waves cross the skin boundary.
Self-check
A reflected ultrasound beam has frequency shift 2.0 kHz from 5.0 MHz, c=1500 m s⁻¹, and θ=0°. Find blood speed.
Show the answer
v=(Δf/f)c/2=(2.0×10³/5.0×10⁶)×1500/2=0.30 m s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M0.1
Open revision guidance
What to know
- Choose units from the defined quantity and convert prefixes before substitution; volume conversions cube the length factor. A result without its unit is not a complete physical answer.
- Convert 250 cm³ to m³ by multiplying by (10⁻²)³; then calculate density with kg/m³ and preserve dimensions through every step.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Prefix conversion applies to each power of a unit, not just its numeral.
Self-check
Convert 250 cm³ to m³.
Show the answer
250×10⁻⁶=2.50×10⁻⁴ m³.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M0.2
Open revision guidance
What to know
- Write very large/small quantities as a×10ⁿ with 1≤|a|<10 and use constants in the same form as the data sheet.
- For multiplication add exponents and multiply coefficients; for division subtract exponents; retain units and check order.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Standard form keeps particle and astronomical scales manageable.
Self-check
Evaluate (3.0×10⁸)(2.0×10⁻⁶).
Show the answer
6.0×10².
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M0.3
Open revision guidance
What to know
- Convert a fraction to a percentage by multiplying by 100; efficiency and uncertainty ratios need numerator/denominator with consistent bases.
- Efficiency=useful output/total input×100%; compare before/after quantities using the same unit.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A percentage says how large a part is relative to a reference amount.
Self-check
A device uses 500 J and gives 350 J useful. Find efficiency.
Show the answer
350/500×100%=70%.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M0.4
Open revision guidance
What to know
- Make order-of-magnitude estimates by decomposing a situation into familiar lengths, masses, times or rates, then compare with a plausible physical limit.
- Estimate first without a calculator, show factors and units, then compare with measured/calculated value and identify which assumption dominates.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
An estimate is a reasonableness check, not an unjustified exact value.
Self-check
Estimate the volume of a 2 m×0.5 m×0.1 m block.
Show the answer
V≈0.10 m³.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M0.5
Open revision guidance
What to know
- Use calculator powers, eˣ, ln and log for energy, oscillation and decay models. Rearrange an exponential before taking logarithms.
- For N=N₀e^(−λt), take ln(N/N₀)=−λt and solve t=−ln(N/N₀)/λ; check that ratio is dimensionless.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A logarithm turns an exponential relationship into a straight-line relation.
Self-check
A sample has 25% left after decay. What is ln(N/N₀)?
Show the answer
ln(0.25)=−1.386.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M0.6
Open revision guidance
What to know
- Choose calculator angle mode correctly; vector components and projectile geometry require sine, cosine or tangent with a stated angle convention.
- Resolve F at angle θ from x using Fx=Fcosθ and Fy=Fsinθ; calculate resultant direction with quadrant-aware inverse tangent.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
The angle unit and direction reference matter as much as the trig key.
Self-check
Resolve 10 N at 30° above x.
Show the answer
Fx=8.66 N; Fy=5.00 N.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M1.1
Open revision guidance
What to know
- Use raw measurement precision and stated uncertainty to limit reported digits; exact counts/constants do not set measurement precision.
- Keep guard digits through calculation, then round once to the least reliable measured precision and carry units.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A calculator’s many digits are not extra experimental information.
Self-check
2.4 m divided by 0.80 s: report speed to appropriate significant figures.
Show the answer
v=3.0 m s⁻¹ (two significant figures).
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M1.2
Open revision guidance
What to know
- The arithmetic mean of repeated values is sum/count; repeated readings estimate scatter, not remove a common systematic error.
- Record every repeat, calculate mean and range/uncertainty, inspect anomalies against a stated rule rather than silently deleting.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Repeats improve evidence about random variation.
Self-check
Times are 1.21, 1.19 and 1.20 s. Find the mean.
Show the answer
Mean=3.60/3=1.20 s.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M1.3
Open revision guidance
What to know
- A single nucleus decays randomly with constant probability per interval; large populations show exponential statistics. Dice/simulated trials model independent chance, not an individual nucleus’s predictable schedule.
- For a class simulation, remove a fixed fraction of remaining dice each round, graph survivors against time and compare with N=N₀e^(−λt); repeat the simulation to show variation.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Random events can make a predictable population trend.
Self-check
Does a nucleus with a 10-year half-life decay exactly 10 years after it forms?
Show the answer
No. Its half-life describes a population probability; an individual decay time is random.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M1.4
Open revision guidance
What to know
- Compare powers of ten before detailed arithmetic; convert units first and assess whether a result is physically plausible.
- Round inputs to one significant figure and calculate the scale; for an age estimate use H₀⁻¹ only after converting H₀ to s⁻¹.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Order-of-magnitude checks catch unit and exponent mistakes.
Self-check
Order of magnitude of 3×10⁸×2×10⁻⁶?
Show the answer
About 10³.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M1.5
Open revision guidance
What to know
- For addition/subtraction combine absolute uncertainty; multiplication/division combine fractional/percentage uncertainty; for powers multiply percentage uncertainty by exponent magnitude. The course does not require rigorous statistics.
- Show uncertainty units; for A=xy calculate ΔA/A≈Δx/x+Δy/y; for A=x² the relative uncertainty doubles. Compare with graph/error-bar estimates.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Uncertainty follows the way measurements combine.
Self-check
A=xy, x=2.0±0.1, y=3.0±0.2. Estimate percentage uncertainty in A.
Show the answer
5%+6.7%≈11.7%; A=6.0 with about 0.7 absolute uncertainty.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M2.1
Open revision guidance
What to know
- Read equality, approximate equality, proportionality, prefixes/subscripts, change symbols and vector notation in a physics expression; distinguish a definition from a measured equality.
- Before rearranging F=Δp/Δt, state that Δp is change in momentum and Δt elapsed time; use ∝ only to compare scaling with other variables fixed.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Symbols compactly state which physical quantities are equal or changing.
Self-check
If F∝1/r², what happens to F when r doubles?
Show the answer
It becomes one quarter as large.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M2.2
Open revision guidance
What to know
- Change the subject while preserving operations; constant-acceleration, energy and wave equations can be linear or quadratic in the unknown.
- For s=ut+½at², move all terms to one side and solve the quadratic; reject a negative time when the physical interval must be positive.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Rearrangement is a model-solving step, not a change in the physics.
Self-check
From v²=u²+2as, make a the subject.
Show the answer
a=(v²−u²)/(2s).
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M2.3
Open revision guidance
What to know
- Insert measured quantities and constants only after unit conversion; retain parentheses and powers and choose the source equation that matches known data.
- For gravity F=GMm/r² convert masses to kg and centre separation to m before substituting; check result dimension and significant figures.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Substitution is reliable only when values describe the same units and conditions.
Self-check
Find momentum of 0.50 kg at 4.0 m s⁻¹.
Show the answer
p=mv=2.0 kg m s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M2.4
Open revision guidance
What to know
- Solve equations including quadratics arising from constant-acceleration motion; select the mathematically valid root using direction, time and boundary conditions.
- For s=ut+½at² identify coefficients, calculate both roots if needed and reject roots inconsistent with the event or stated positive direction.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Physics conditions decide which mathematical solution describes the experiment.
Self-check
A body starts from rest, falls 1.25 m with g=10 m s⁻². Find time.
Show the answer
1.25=5t², so t=0.50 s (positive root).
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M2.5
Open revision guidance
What to know
- Logarithms represent several orders of magnitude and linearise exponential decay; distinguish ln from log₁₀ and note the axis base.
- For y=y₀e^(−t/τ), ln y=ln y₀−t/τ; gradient of ln y against t is −1/τ.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A log axis spreads out small values and compresses large ones.
Self-check
An ln(signal)–time graph gradient is −0.20 s⁻¹. Find τ.
Show the answer
τ=−1/gradient=5.0 s.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.1
Open revision guidance
What to know
- Move between a physical equation, a plotted relationship and numerical slope/intercept; identify which variable belongs on each axis.
- For F=kx, plot F against x: gradient k. For a stress–strain graph, determine E from slope in elastic region and respect axis units.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A graph is an equation made visible through measured points.
Self-check
A force-extension graph has gradient 40 N m⁻¹. What does the gradient represent?
Show the answer
The spring force constant k=40 N m⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.2
Open revision guidance
What to know
- Plot measured pairs with a useful scale, independent variable on horizontal axis, labelled quantity/unit and uncertainty bars where appropriate.
- For a wire, plot extension against force or force against extension as required; state which slope is being used and fit a line only in the proportional range.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A correct graph makes patterns and anomalies visible.
Self-check
What must a graph axis label include?
Show the answer
The physical quantity and its unit, e.g. extension / m.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.3
Open revision guidance
What to know
- Use gradient and intercept as model parameters; compare a rearranged physical equation with y=mx+c.
- For v=u+at, graph v against t: gradient a and intercept u; use the fit to predict a later value.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A straight line encodes a constant rate of change.
Self-check
For a v–t graph with gradient 2.0 m s⁻² and intercept 3.0 m s⁻¹, write v(t).
Show the answer
v=3.0+(2.0)t, with t in seconds.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.4
Open revision guidance
What to know
- Calculate gradient using well-separated points on the best-fit line; read intercept at the axis, not from arbitrary noisy raw points.
- Record rise/run units and connect intercept to the initial condition, e.g. initial velocity on a velocity–time graph.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Slope measures a relationship’s rate; intercept gives its starting offset.
Self-check
A fitted v–t line crosses v-axis at 4 m s⁻¹. What is initial velocity?
Show the answer
4 m s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.5
Open revision guidance
What to know
- For a linear relation, gradient is constant rate of change and has units y-unit/x-unit.
- Select two points on fitted v–t line and calculate Δv/Δt to find acceleration; include sign.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
The graph’s slope is the physical rate.
Self-check
Velocity changes from 2 to 14 m s⁻¹ in 4 s. Find acceleration.
Show the answer
a=(14−2)/4=3.0 m s⁻².
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.6
Open revision guidance
What to know
- A tangent to a curve approximates local gradient; tangent slope on displacement–time graph gives instantaneous velocity.
- Draw tangent at the requested instant, choose two distant points on the tangent (not the curve), calculate Δs/Δt and state uncertainty from drawing.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A tangent zooms in on the changing rate at one moment.
Self-check
A tangent rises 1.2 m over 0.40 s. Find velocity at that instant.
Show the answer
v≈1.2/0.40=3.0 m s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.7
Open revision guidance
What to know
- Average rate uses total change/time interval; instantaneous rate is local gradient at a point.
- Compare secant slope between two graph points with tangent slope at a particular time; identify which question asks for each.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Average describes a whole interval; instantaneous describes one moment.
Self-check
What gives instantaneous velocity from a displacement-time curve?
Show the answer
The gradient of a tangent at the chosen time.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.8
Open revision guidance
What to know
- Area between graph and x-axis can represent physical quantities, including displacement, impulse and capacitor energy; use signed area where required.
- Divide non-linear area into trapezia/triangles or count squares, refine intervals and preserve sign; state physical meaning and units.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Area combines the plotted quantity over time or another independent variable.
Self-check
A constant 5 N force acts for 0.20 s. Find area under F–t graph and its meaning.
Show the answer
Area=1.0 N s, equal to impulse/change in momentum.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.9
Open revision guidance
What to know
- Interpret a rate equation and solve via finite intervals, graph gradient or spreadsheet iteration; no explicit derivative/integral notation is required.
- Use Δx/Δt≈−λx on short steps or fit a curved measurement; for capacitor/radioactive model compare numerical data with the predicted decay.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A changing quantity’s rate depends on the current value in exponential decay.
Self-check
If dN/dt=−0.10N per second at N=500, what is the instantaneous rate?
Show the answer
−50 nuclei s⁻¹ (model rate at that instant).
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.10
Open revision guidance
What to know
- Read slope and intercept on log plots and connect them to the physical exponential parameters.
- For ln V against t, gradient=−1/RC and intercept=ln V₀; calculate τ from slope and use residuals to assess model fit.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A straight log plot indicates an exponential relation under the chosen axes.
Self-check
An ln V–t gradient is −0.50 s⁻¹. Find RC.
Show the answer
RC=−1/(−0.50)=2.0 s.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.11
Open revision guidance
What to know
- Transform data appropriately: exponential y=y₀e^(kx) is linear on ln y vs x; power y=axⁿ is linear on log y vs log x.
- Plot transformed data, label base and units, fit line and infer exponent/slope; compare with model and measurement range.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A straight transformed graph tests a proposed mathematical pattern.
Self-check
A log y–log x graph has slope 2. What power law does it support?
Show the answer
y∝x².
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M3.12
Open revision guidance
What to know
- Recognise inverse, direct, squared, reciprocal-squared, sine, cosine, squared trig and exponential shapes from y=k/x, kx, kx², k/x², sin x, cos x, e±x, sin²x and cos²x.
- Mark intercepts, asymptotes, periodicity and increasing/decreasing direction before sketching; attach the correct physical domain.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Shape communicates a model even when no numerical scale is given.
Self-check
Sketch qualitatively capacitor discharge V=V₀e^(−t/RC).
Show the answer
It starts at V₀, decreases exponentially and approaches zero asymptotically.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M4.1
Open revision guidance
What to know
- Identify interior angles and geometrical relationships in regular shapes and three-dimensional force diagrams.
- Draw the geometry in a plane of action, mark equal/known angles, and use triangle/shape sums before resolving forces.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Correct geometry prevents a force from being resolved along the wrong direction.
Self-check
Three equal forces meet at a point with 120° between each. Can they balance?
Show the answer
Yes; their vector sum is zero by symmetry.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M4.2
Open revision guidance
What to know
- Translate a 3-D object into a labelled 2-D diagram, showing axes, depth, forces and line of sight needed for calculation.
- Draw a free-body diagram or vector triangle with appropriate projection; mark perpendicular sides and distinguish actual from projected lengths.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
A clear sketch makes hidden directions calculable.
Self-check
Why draw a free-body diagram before summing forces?
Show the answer
It identifies all forces on the selected object and their directions.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M4.3
Open revision guidance
What to know
- Calculate triangle area ½bh; circle circumference 2πr and area πr²; rectangular-block volume lwh; cylinder curved surface area 2πrh and volume πr²h; sphere surface area 4πr² and volume 4πr³/3. Choose geometry appropriate to the physical measurement.
- For a wire diameter use A=πd²/4; for a rectangular sample use cross-section width×thickness. Convert all lengths to SI before using resistivity, density or mass.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Geometry determines how much material or area a physical process involves.
Self-check
A wire diameter is 2.0 mm. Find its cross-sectional area.
Show the answer
A=π(1.0×10⁻³)²=3.14×10⁻⁶ m².
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M4.4
Open revision guidance
What to know
- For perpendicular components R=√(x²+y²); use triangle angle sum and direction to solve vector geometry.
- Resolve, calculate magnitude and use correct quadrant for direction; check the components reconstruct the resultant.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Pythagoras combines perpendicular components into one magnitude.
Self-check
Components are 6 N east and 8 N north. Find resultant magnitude.
Show the answer
R=√(6²+8²)=10 N.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M4.5
Open revision guidance
What to know
- Use SOHCAHTOA with angle defined to the stated axis; choose calculator degrees/radians as appropriate.
- Resolve a projectile’s launch velocity and solve time from vertical motion before horizontal range; state signs and use same time.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Trig connects direction with perpendicular components.
Self-check
A 20 m s⁻¹ launch is at 30° above horizontal. Find vertical component.
Show the answer
uy=20sin30°=10 m s⁻¹.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M4.6
Open revision guidance
What to know
- For a small angle measured in radians, sinθ≈tanθ≈θ and cosθ≈1; these simplify distant-screen interference geometry.
- Use θ≈x/D when x≪D, then substitute into d sinθ=nλ to derive fringe spacing; compare approximation with exact trig if angle is not small.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
For a small angle, arc and tangent are nearly the same length ratio.
Self-check
At θ=0.020 rad, estimate sinθ.
Show the answer
sinθ≈0.020.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5e M4.7
Open revision guidance
What to know
- One full turn is 360°=2π rad; radians=degrees×π/180 and degrees=radians×180/π.
- Convert before using ω=2π/T or angular displacement; do not insert degrees into radian-only approximations.
What to do in an assessment
- Write the governing operation with units before substituting and show the intermediate result.
- Use the example calculation to check sign, scale, precision and model assumptions.
In plain language
Radians compare angle directly with arc length/radius.
Self-check
Convert 90° to radians.
Show the answer
90×π/180=π/2 rad.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW1
Open revision guidance
What to know
- A model or theory connects observations to a causal physical explanation and makes testable predictions. Newtonian particle, field and wave models each have defined assumptions and limits.
- Compare an observed result with a prediction from the model, state the assumption (for example negligible drag), and identify an observation that would falsify it.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
Why is a frictionless projectile calculation a model rather than a literal description?
Show the answer
It assumes drag is negligible; measurements can test whether that approximation is adequate.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW2
Open revision guidance
What to know
- Use physics knowledge to pose a measurable scientific question, define a problem, construct an evidence-based argument and communicate scientific ideas.
- Turn “which material is best?” into a specified performance measure, conditions and controlled comparison; write a claim, evidence and reasoning chain.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
What must be specified to test whether a wire stretches more than another?
Show the answer
Force range, extension measurement, sample geometry/material, control conditions and uncertainty.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW3
Open revision guidance
What to know
- Select a method that answers the question; use ICT/data logging/spreadsheets/software to collect, process, model or report data while preserving provenance.
- Choose sampling rate above the changing signal’s timescale, store raw data and metadata, use a formula/graph transparently and check output against an independent calculation.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
Why record the sensor range and sampling interval with a logger file?
Show the answer
They are needed to interpret resolution, response and whether rapid changes were missed.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW4
Open revision guidance
What to know
- Conduct experimental/investigative activities in varied contexts using appropriate apparatus, sequence and proportionate risk controls.
- Identify hazards and who/what can be harmed, reduce exposure/energy, inspect equipment, follow the method and stop if controls fail.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
Name controls for an ionising-radiation demonstration.
Show the answer
Use an approved sealed source and detector, maximise distance, minimise time, use shielding, and follow local rules/supervision.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW5
Open revision guidance
What to know
- Analyse and interpret data as evidence, recognise correlations and evaluate whether a causal explanation is justified.
- Plot relevant axes, quantify gradient/uncertainty, compare a predicted relationship and consider confounding variables before stating causation.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
If temperature and resistance rise together, what is needed before claiming temperature caused the change?
Show the answer
Control other conditions such as geometry/contact and repeat measurements over a defined range.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW6
Open revision guidance
What to know
- Evaluate methodology, evidence and data quality and reconcile conflicting results by comparing assumptions, controls, uncertainty and independent tests.
- Compare resolution, calibration, sample size, conditions and model scope; identify an experiment that discriminates between explanations.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
Two values of g differ by 5%. What should be compared first?
Show the answer
Timing/length calibration, release method, uncertainty and whether both use the same free-fall conditions.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW7
Open revision guidance
What to know
- Scientific knowledge changes through new observation, improved technology, testing and replacement/refinement of models.
- Trace a claim from earlier model to evidence that challenged it and the current model; distinguish historical development from a simple progress story.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
What evidence challenged the simple atom model?
Show the answer
Large-angle alpha scattering required a concentrated, positively charged nucleus.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW8
Open revision guidance
What to know
- Communicate information for audience and purpose using appropriate terms, labelled diagrams, graphs, units, uncertainty and a traceable conclusion.
- Select a table/graph/equation suited to data; define symbols, label axes quantity/unit and distinguish observation from inference.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
What should accompany a value for Young modulus in a report?
Show the answer
The unit Pa, method/data range, appropriate significant figures and an uncertainty or limitations statement.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW9
Open revision guidance
What to know
- Consider applications and implications of physics and weigh benefits against physical, environmental, financial or societal risks.
- Compare options using the same criteria and evidence; identify who benefits, who bears risk, uncertainty and available mitigation.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
What should a decision about a satellite include besides its communications benefit?
Show the answer
Cost, coverage, launch/debris risks, reliability and alternative technologies.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW10
Open revision guidance
What to know
- Consider ethical issues in treatment of people, organisms and environment, including consent, privacy, radiation exposure, fairness and alternatives.
- Identify affected stakeholders, expected benefit, possible harm and consent/privacy safeguards; state uncertainty rather than treating a technical result as a moral decision.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
What ethical trade-off arises in PET diagnosis?
Show the answer
Potentially valuable diagnostic information must be balanced against tracer/radiation risk, consent and availability.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW11
Open revision guidance
What to know
- The scientific community validates knowledge through transparent methods, repeatability, peer scrutiny, traceable data and correction of error.
- Check source quality, method disclosure, data availability and independent replication; identify conflicts of interest or selective reporting.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
Does peer review alone prove an experimental claim true?
Show the answer
No; repeatable evidence and ongoing scrutiny are also needed.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5d HSW12
Open revision guidance
What to know
- Society uses scientific evidence to make individual and collective decisions; scientific advice informs but does not replace values, costs and policy choices.
- State evidence, uncertainty and values separately; compare alternatives, affected groups and long-term consequences before recommending action.
What to do in an assessment
- Apply this reasoning to a source-specific physics case; state evidence, uncertainty and the decision/reasoning step.
- Separate measured observation, model inference and value judgement in the written response.
In plain language
How Science Works connects physical evidence to explanations and decisions.
Self-check
Why can two communities choose different energy policies using the same physics data?
Show the answer
They may weigh cost, reliability, environmental risk and social priorities differently.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG1
Open revision guidance
What to know
- Use analogue apparatus for distance, angle and mass with interpolation; stopwatch/light gates, ICT/data logger/video, and set square/plumb line improve motion measurement. Example: acceleration due to free fall.
- Release a trolley/body consistently, measure distances and repeated times or gate speeds, record sensor/range metadata and fit motion data; use repeated intervals and geometric alignment to reduce error.
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
A motion practical links measured time and distance to kinematics while preserving uncertainty.
Self-check
How can a light gate give speed for a card of known length?
Show the answer
Divide card length by beam-interruption time; repeat and include card-length and timing resolution.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG2
Open revision guidance
What to know
- Use vernier/digital calipers or micrometer for small distances, analogue length measurement/interpolation, digital mass measurement; example: Young modulus of a metal.
- Measure wire length/diameter at multiple sites, apply known loads below damage, measure extension, plot F–x and calculate E=(L/A)(ΔF/ΔL).
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
Small diameter uncertainty is important because cross-sectional area depends on diameter squared.
Self-check
Why take multiple diameter readings along a wire?
Show the answer
The wire may vary in diameter and a diameter error is doubled approximately in the area’s percentage uncertainty.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG3
Open revision guidance
What to know
- Use multimeters for current, voltage and resistance; calipers/micrometers for dimensions and correct DC circuit construction. Example: metal resistivity or conductivity.
- Wire current meter in series and voltmeter in parallel, vary current safely, obtain R from V/I or graph, measure L and d, then calculate ρ=RA/L.
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
Electrical properties are inferred from readings whose circuit position and geometry are known.
Self-check
What is the main circuit-position difference between ammeter and voltmeter?
Show the answer
Ammeter series; voltmeter parallel across the component.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG4
Open revision guidance
What to know
- Use digital meters, construct correctly polarised DC circuits, and design/check a circuit; example: sensor potential divider.
- Build a fixed resistor plus LDR/thermistor divider, measure supply and output over known light/temperature values, inspect range and calibration, then test open/short faults safely.
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
A sensor circuit maps a physical input into a voltage response.
Self-check
If an LDR is the lower leg of a divider, what happens to output across it as light increases?
Show the answer
Its resistance falls, so its share of the total voltage falls.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG5
Open revision guidance
What to know
- Use analogue length/angle measurements, oscilloscope/signal generator V/div and time-base, microphone/speaker, ripple tank, transducer or microwave/radio source, laser/light and ICT. Examples include two-source superposition and wavelength determination.
- Set source frequency and detector geometry, map nodes/fringes, measure multiple spacings, and use v=fλ or x=λD/a; control alignment and report uncertainty.
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
Wave patterns reveal frequency, wavelength and superposition through measurable geometry.
Self-check
How can counting several fringes improve a wavelength estimate?
Show the answer
Measure total span across many fringe separations and divide by their number, reducing endpoint uncertainty per spacing.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG6
Open revision guidance
What to know
- Use appropriate digital multimeters for current/voltage, correctly polarised circuits and methods that improve measurement accuracy. PAG6 also requires a laser or light source to investigate light characteristics including interference and diffraction; its example activity determines Planck’s constant using LEDs.
- For LED work, measure threshold voltage for LEDs of different wavelength, repeat readings, identify frequency and fit energy versus frequency. For the light-characteristics technique, use a laser with a double slit or diffraction grating; measure fringe spacing or grating angle and infer wavelength. Control ambient light, avoid over-driving LEDs and follow laser safety controls.
What to do in an assessment
- Use a laser to illuminate a double slit or grating; measure multiple fringe spacings or maxima angles with a calibrated scale, repeat/alignment-check readings and calculate wavelength using x=λD/a or d sinθ=nλ. Also assemble the LED circuit with correct polarity and measure current/threshold voltage accurately.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
A multi-colour trend is stronger evidence for h than a single LED threshold.
Self-check
What graph gradient gives h when photon energy in joules is plotted against frequency?
Show the answer
Gradient ΔE/Δf=h.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG7
Open revision guidance
What to know
- Use suitable alpha/beta/gamma detectors and ICT/data logging; example: absorber investigation. Safety and controlled exposure are central.
- Measure background first; keep source-detector geometry fixed, add absorbers stepwise, count for equal intervals, subtract background and compare penetration/range.
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
Counts fluctuate statistically, so longer repeats improve the estimate but do not license unsafe source handling.
Self-check
Why measure background before source counts?
Show the answer
To separate ambient count rate from source contribution.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG8
Open revision guidance
What to know
- Use analogue pressure, volume and temperature measurement with scale interpolation. Example: gas temperature versus pressure extrapolation.
- Trap a fixed amount of gas, vary temperature after thermal equilibrium, record pressure at controlled volume, graph pressure against Celsius temperature and extrapolate to zero pressure cautiously.
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
A zero-pressure extrapolation estimates absolute zero under an ideal-gas model.
Self-check
Why wait for thermal equilibrium before recording pressure?
Show the answer
Gas pressure and thermometer reading must represent the same stable temperature.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG9
Open revision guidance
What to know
- Use multimeters for current/voltage/resistance, digital time measurement, designed circuits, ICT/logger; examples: capacitor combinations and time constant from ln V–time slope.
- Measure C combinations in safe low-voltage circuits, record charging/discharging V or I versus time, graph ln(signal) against t and find τ=−1/gradient; compare with RC.
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
The exponential time trace tests the RC model quantitatively.
Self-check
What is the gradient of ln V against time during ideal discharge?
Show the answer
−1/RC.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG10
Open revision guidance
What to know
- Use digital time measurement, analogue distance, multiple oscillations/fiducial marks and ICT; example: investigate factors affecting oscillator period.
- Time many cycles, divide by count, repeat for changed mass/length/amplitude as applicable, graph T or T² against the chosen variable, and control pivot/geometry.
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
Repeating cycles reduces reaction-time uncertainty in one-period timing.
Self-check
A pendulum takes 20.0 s for 10 cycles. Find its period.
Show the answer
T=20.0/10=2.00 s.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG11
Open revision guidance
What to know
- Apply investigative approaches in a real context; a suitable example is specific heat capacity of a material. Plan variable range, apparatus, calibration, safety, repeats and a valid analysis before collecting data.
- Design an electrical heating method: measure mass, V, I and temperature-time; account for heat loss, use a control/insulation or cooling correction, calculate c=VIt/(mΔT), and evaluate dominant uncertainty.
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
An open investigation tests whether the learner can choose and justify a method, not merely follow a recipe.
Self-check
What evidence would show that electrical heating energy was not all retained by a block?
Show the answer
Temperature rise is lower than VIt predicts; heat escapes to surroundings or apparatus, so method needs insulation/correction.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5g Table 1 PAG12
Open revision guidance
What to know
- Use online/offline sources such as textbooks and scientific websites, correctly cite information; source examples include GPS operating principles and radioactive tracers in imaging.
- Check author/date/source and compare independent references, distinguish established evidence from claims, record enough citation detail and paraphrase accurately.
What to do in an assessment
- Use the stated PAG apparatus and method to obtain raw data, retaining calibration/range and control details.
- Process the readings with the named physics relationship, evaluate uncertainty and document safe handling; this teaches the activity but does not award or predict a Practical Endorsement pass.
In plain language
Research is useful only when its source and reasoning can be checked.
Self-check
What details let a reader retrieve a cited online source?
Show the answer
Author/organisation, page or title, URL and access/date information consistent with the citation convention.
- Core
Open revision guidance
What to know
- Use the printed values g=9.81 m s⁻², e=1.60×10⁻¹⁹ C, c=3.00×10⁸ m s⁻¹, h=6.63×10⁻³⁴ J s, N_A=6.02×10²³ mol⁻¹, R=8.31 J mol⁻¹ K⁻¹, k=1.38×10⁻²³ J K⁻¹, G=6.67×10⁻¹¹ N m² kg⁻², ε₀=8.85×10⁻¹² F m⁻¹, mₑ=9.11×10⁻³¹ kg, mₚ=1.673×10⁻²⁷ kg, mₙ=1.675×10⁻²⁷ kg, mα=6.646×10⁻²⁷ kg and σ=5.67×10⁻⁸ W m⁻² K⁻⁴. Values are generally printed to three significant figures unless more/fewer are useful.
- Quark charges: u=+2e/3; d=s=−e/3; antiparticle signs reverse. Convert 1 u=1.661×10⁻²⁷ kg, 1 eV=1.60×10⁻¹⁹ J, 1 day=8.64×10⁴ s, 1 year≈3.16×10⁷ s, 1 ly≈9.5×10¹⁵ m and 1 pc≈3.1×10¹⁶ m.
What to do in an assessment
- Select the relevant supplied constant and retain its units; convert eV/u/time/distance before combining with SI equations.
- Check whether a mass is electron, proton, neutron or alpha; use the matching value and precision rather than a remembered substitute.
In plain language
Constants and conversions have units that are part of their meaning.
Self-check
Convert 2.0 eV into joules using the data sheet.
Show the answer
E=2.0×1.60×10⁻¹⁹=3.20×10⁻¹⁹ J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5c mathematical equations: geometry, trigonometry and logarithms (pp.63–64)
Open revision guidance
What to know
- Use arc length rθ, circle circumference 2πr/area πr², cylinder curved area 2πrh and volume πr²h, sphere surface area 4πr²/volume 4πr³/3, trapezium area ½(a+b)h, Pythagoras and sine/cosine rules.
- Use small-angle sinθ≈tanθ≈θ and cosθ≈1 only for θ in radians; logarithm rules log(AB)=logA+logB, log(A/B)=logA−logB, log(xⁿ)=nlogx, and ln(eˣ)=x.
What to do in an assessment
- Check geometry variables (radius versus diameter, area versus volume) and convert length to SI before applying relationships.
- For exponential graphs take natural logs of dimensionless ratios; state angle units before applying small-angle approximations.
In plain language
These mathematical relationships supply geometry and transformations used by physics models.
Self-check
A circle has radius 0.20 m. Find its area and circumference.
Show the answer
A=πr²=0.126 m²; C=2πr=1.26 m.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5c Module 2–3 relationships (pp.64–65)
Open revision guidance
What to know
- Module 2: resolve vectors Fx=Fcosθ, Fy=Fsinθ. Module 3: v=u+at, s=(u+v)t/2, s=ut+½at², v²=u²+2as; F=Δp/Δt, p=mv; moment=Fx, couple torque=Fd; ρ=m/V, p=F/A, liquid p=ρgh.
- Also W=Fxcosθ, efficiency=useful/total×100%, P=W/t and P=Fv; spring F=kx, elastic E=½Fx=½kx²; stress=F/A, strain=x/L, Young modulus E=stress/strain.
What to do in an assessment
- Choose the relation that matches known variables, rearrange before substitution, define signs and check dimensions/conditions such as constant acceleration or uniform g.
- Identify the system, select a model, calculate with SI units and compare a result against an independent graph or limiting case.
In plain language
The data sheet gives relationships; the learner still chooses and interprets the appropriate model.
Self-check
Which data-sheet equation gives displacement when u, a and t are known under constant acceleration?
Show the answer
s=ut+½at².
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5c Module 4 relationships (pp.65–66)
Open revision guidance
What to know
- Charge/current I=ΔQ/Δt, I=Anev; work W=VQ=EQ=VIt; R=ρL/A; series/parallel resistor rules; P=VI=I²R=V²/R; E=I(R+r)=V+Ir; divider Vout=R₂/(R₁+R₂)Vin and V₁/V₂=R₁/R₂.
- Wave v=fλ, f=1/T, I=P/A, Young fringes x=λD/a, refraction n=c/v and Snell/critical-angle rules; photons E=hf=hc/λ, hf=φ+KEmax, de Broglie λ=h/p.
What to do in an assessment
- Check circuit topology and graph axes before use; for eV and wavelength convert to SI, and distinguish photon energy from beam intensity.
- For Young fringes measure x and D, know slit separation a and calculate λ=xa/D; use small-angle condition a≪D.
In plain language
Electrical and quantum formulae connect charge flow, waves and energy transfer.
Self-check
A 600 nm photon has what energy using h=6.63×10⁻³⁴ J s and c=3.00×10⁸ m s⁻¹?
Show the answer
E=hc/λ=3.32×10⁻¹⁹ J.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5c Module 5 relationships (pp.66–67)
Open revision guidance
What to know
- Thermal E=mcΔT and E=mL; ideal gas pV=NkT=nRT=(1/3)Nm⟨c²⟩, ½m c_rms²=3/2kT and mean translational energy 3/2kT per molecule. Circular ω=2π/T=2πf, v=ωr, a=v²/r=ω²r and F=mv²/r=mω²r.
- SHM ω=2π/T=2πf, a=−ω²x, x=Acosωt or Asinωt, v=±ω√(A²−x²). Gravity g=F/m, F=GMm/r², g=GM/r², T²=4π²r³/(GM), Vg=−GM/r and Ep=−GMm/r. Stellar equations: hf=ΔE=hc/λ, d sinθ=nλ, λmaxT=b, L=4πR²σT⁴; cosmology adds Doppler shift, parallax p=1/d, v≈H₀d and t≈H₀⁻¹.
What to do in an assessment
- Select the thermal/gas/circular/oscillation/gravity/radiation relation from measured quantities; state the model assumptions and units.
- Convert H₀ to s⁻¹ before estimating Hubble time; use absolute temperature and centre-to-centre radius where required.
In plain language
Thermal, orbital and astronomical calculations use connected models but different assumptions.
Self-check
If H₀=2.0×10⁻¹⁸ s⁻¹, estimate Hubble time.
Show the answer
t≈1/H₀=5.0×10¹⁷ s.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5c Module 6 relationships (pp.67–68)
Open revision guidance
What to know
- Capacitors: C=Q/V, C=ε₀A/d, C=4πε₀R, series/parallel rules; W=½QV=Q²/(2C)=½CV²; τ=RC and exponential charge/discharge. Electric: E=F/q, F=Qq/(4πε₀r²), E=Q/(4πε₀r²) or V/d, V=Q/(4πε₀r), U=Qq/(4πε₀r).
- Magnetic: F=BILsinθ and Bqv; Φ=BAcosθ, emf=−Δ(NΦ)/Δt, transformer Ns/Np=Vs/Vp=Ip/Is. Nuclear: R=r₀A^(1/3), A=λN, dN/dt=−λN, λt½=ln2, A=A₀e^(−λt), N=N₀e^(−λt), ΔE=Δmc². Imaging: I=I₀e^(−μx), Z=ρc, Ir/I₀=[(Z₂−Z₁)/(Z₂+Z₁)]², Δf/f=2vcosθ/c.
What to do in an assessment
- Check whether the field is uniform or radial, whether a relation uses flux or flux linkage and whether radiation intensity or dose is being calculated.
- For RC/radioactive decay linearise ln(signal) against time; for ultrasound use echo time and Doppler angle with the correct sound speed.
In plain language
The final module uses distinct electrical, magnetic, nuclear and imaging models.
Self-check
An ideal 10:1 step-down transformer has 240 V primary. Find the secondary voltage.
Show the answer
Vs/Vp=Ns/Np=1/10, so Vs=24 V.
- Core
Scope: Core · OCR H556 Version 3.0 (March 2026), Appendix 5f Health and Safety (pp.77–78)
Open revision guidance
What to know
- The employer is responsible for risk assessment; review model assessments for the actual room, equipment, scale and learner capability and communicate significant point-of-use controls.
- Novel/project procedures may not be covered by model assessment; obtain appropriate employer guidance before proceeding. Controls are activity-specific, not a substitute for local rules.
What to do in an assessment
- Identify hazard, harm, exposure and controls; reduce scale/energy/exposure, use shielding/eye protection/electrical isolation as appropriate and record local modifications.
- Before radiation, high-voltage, laser or hot-material activity verify approved apparatus and context-specific controls; stop if controls are inadequate.
In plain language
A safe practical adapts controls to the actual activity instead of copying a generic sheet blindly.
Self-check
What should happen if a novel practical is not covered by the employer’s model risk assessment?
Show the answer
Stop before the activity and obtain the employer’s appropriate safety guidance/review; do not assume the model assessment covers it.
Verified qualification
OCR A-Level: Physics B (Advancing Physics) (H557)
Exam years · 2027Specification version · Version 2.9 (March 2026)
Course details
Assessment For assessment details, see the official specification.
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Reviewed course guidance
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Open a point to read what to know, how to use it in an assessment, a plain-language explanation and a self-check. Answers stay hidden until you choose to reveal them.
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Topic group
Reviewed requirements
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §1.1.1(a)-(c); 1.1.2(a)-(c)
Open revision guidance
What to know
- Plan a test by translating physics into a measurable independent variable, dependent response and relevant controls; select apparatus, range, resolution, safety controls and a repeatable sequence. Predict the scale of the result from the model and reject a method if its expected signal is smaller than instrument resolution or uncertainty.
- Implement safely and follow instructions; record raw observations with units/precision, then process and interpret qualitative/quantitative results. Evaluate whether evidence answers the question, distinguish conclusion validity from measurement quality and propose a specific improvement linked to a limitation.
What to do in an assessment
- For a proposal, state independent/dependent/control variables, apparatus range and resolution, safety, repeats, expected graph/model and why the method can distinguish predicted outcomes; choose detector response time short compared with the physical change.
- Present raw data first, show one worked processing step and uncertainty, plot appropriate variables, compare result with the predicted relationship and propose a targeted change (e.g. light gates rather than a hand stopwatch for millisecond motion).
In plain language
The written-paper practical skill is to justify why a method can answer the question, not merely recite apparatus names.
Self-check
Why hold a sensor's response time in mind when measuring a rapidly changing signal?
Show the answer
The sensor may lag behind the physical change, so its displayed value may not represent the instantaneous signal.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §1.1.3(a)-(d)(i)-(ii); 1.1.4(a)-(e); Module 2(a)-(c)(i)-(iii)
Open revision guidance
What to know
- Distinguish accuracy from precision, resolution, sensitivity, response time, random spread and systematic/zero error; identify the largest uncertainty source. Display repeats as a dot plot, estimate mean or median and range/spread, flag an outlier and suggest an apparatus/procedure cause.
- Choose a scatter, bar/pie or logarithmic plot to suit the variables; label quantities, units and scales, add uncertainty bars, and inspect whether the model is supported. Report appropriate significant figures. Find percentage uncertainty as Δx/x×100%; combine absolute uncertainties for sums/differences and use fractional/percentage contributions for products, quotients and powers, then test extreme values for the largest uncertain input.
- For a best-fit gradient, draw plausible steepest/shallowest lines through uncertainty bars; report the gradient range or half-range as an estimate of gradient uncertainty. Estimate intercept uncertainty the same way. Use SI prefixes, standard form, radians/degrees and order-of-magnitude checks consistently.
What to do in an assessment
- For repeats 9.8, 10.0, 10.1 and 14.0 cm, plot every value, calculate the mean/median and range, investigate whether 14.0 cm is a recording or method anomaly, and do not discard it without justification.
- For y=x₁+x₂ add absolute uncertainties; for z=x₁x₂ estimate fractional/percentage uncertainty contributions, and calculate upper/lower results using the extreme input values. Plot data with axis units and uncertainty bars, draw a best-fit line and plausible extreme gradients, then state how that uncertainty affects the conclusion.
In plain language
A narrow spread does not rule out a shared systematic error; a graph and uncertainty estimate show different parts of measurement quality.
Self-check
A length is 50.0±0.5 mm. What is its percentage uncertainty?
Show the answer
(0.5/50.0)×100=1.0%.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §1.2.1(a)-(j); 1.2.2(a)-(l); 5h Table 1 PAG1-PAG12
Open revision guidance
What to know
- Choose an analogue or digital range that spans the expected value without over-ranging; use the smallest suitable range to improve resolution, check zero/calibration and record range, resolution and units. On an analogue scale interpolate between marked divisions (e.g. estimate tenths of a 1-unit division); read a digital instrument to its last displayed digit and account for its resolution.
- Use a set square to establish perpendicular alignment and a plumb line for verticality; time many oscillations or use a fiducial marker to reduce fractional timing uncertainty. Measure length/distance, temperature, pressure, force, angles and volume with appropriate analogue apparatus; time, current, voltage, resistance and mass with digital instruments/multimeters.
- For a vernier caliper, close and check zero, measure with suitable jaws, read the main scale before the vernier zero and add the aligned vernier division×least count; for a micrometer, use the ratchet, add sleeve and thimble readings and apply zero correction. Repeat small-dimension readings at multiple orientations/positions.
- Construct circuits from diagrams with DC supply/cells and polarity-sensitive components checked; isolate power before changing wiring. For oscilloscopes set volts/division and time-base, centre/trigger the trace, read peak-to-peak voltage from vertical divisions and period from horizontal divisions; use a signal generator and microphone/loudspeaker, ripple tank, vibration transducer or microwave/radio source to generate/measure waves.
- Use lasers/light sources for interference and diffraction; ICT/data loggers with sensors for collection, modelling and processing; and radiation detectors with appropriate safety controls. Across the course, follow instructions, keep records, present data scientifically and choose suitable kit. Component /04 requires at least 12 assessed practicals and CPAC evidence; a written guide cannot attest to actual learner competence.
What to do in an assessment
- For each reading state expected range, instrument resolution, how the scale is interpolated and how zero/position error is controlled. In a vernier example with 1 mm main divisions and 0.1 mm least count, a zero after 12 mm plus the 6th coincident division reads 12.6 mm before zero correction.
- On an oscilloscope, if one cycle spans 4.0 divisions at 0.50 ms/division, T=2.0 ms and f=500 Hz; if its height is 3.0 divisions at 2.0 V/division, Vpp=6.0 V. Present raw data, processed results, uncertainty and evidence-based conclusion.
In plain language
A written practical question assesses method reasoning; it cannot itself demonstrate every hands-on competency.
Self-check
Does completion of one PAG experiment establish a pass in the Practical Endorsement?
Show the answer
No. OCR requires practical evidence across the activity groups and teacher assessment against CPAC; the endorsement is separately reported.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §3.1.1(a)(i)-(iv); 3.1.1(b)(i)-(iii)
Open revision guidance
What to know
- A thin converging lens forms a real image by changing wavefront curvature. Computer images are arrays of pixel values that can be manipulated for brightness, contrast, noise reduction, edge detection or false colour. Digitising samples a signal and assigns finite levels; this enables storage/transmission but can lose detail. A byte is 8 bits, so 24 bits of pixel data occupy 3 bytes before metadata or compression.
- Use ray and wavefront diagrams; distinguish signal from noise, pixel from bit and sampling frequency from bit depth. Polarisation is evidence of transverse electromagnetic waves: rotate a polarising sheet between a lamp and detector and observe transmitted intensity; for microwaves, rotate a wire-grid polariser/receiver and compare signal at different orientations. A longitudinal wave cannot show this orientation-dependent transmission.
- An analogue-to-digital converter samples voltage and rounds each sample to one of a finite set of amplitude levels. If an 8-level display spans 0–8 V, its 1 V step gives a staircase representation; a 3.4 V sample is recorded at the nearest available level and incurs quantisation error. Increasing resolution adds levels and reduces that error.
What to do in an assessment
- Determine focal length/power practically: point a converging lens at a distant object, move a screen until its sharp image forms, measure lens-to-screen distance f and calculate P=1/f in dioptres; alternatively measure several u,v pairs and test 1/f=1/u+1/v.
- Rotate a light polariser or microwave grid and record detector intensity against angle. For a digitised waveform, mark each sample time, round its measured voltage to the nearest ADC level and sketch the resulting staircase; compare it with the original trace.
In plain language
More bits give more brightness levels per pixel, while more pixels give spatial samples; these are different improvements.
Self-check
What information is lost when an analogue signal is represented with too few samples?
Show the answer
Rapid changes above the sampling limit are not represented faithfully and can be misidentified as slower frequencies.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §3.1.1(c)(i)-(x); 3.1.1(d)(i)-(ii); Data, Formulae and Relationships booklet
Open revision guidance
What to know
- Image information is pixels×bits per pixel; b bits encode N=2ᵇ levels. For the specification's noise limit on bits per sample, b=log₂(Vtotal/Vnoise): use the total signal range and noise voltage in the same units before taking the base-2 logarithm. Sampling rate must exceed twice the highest signal frequency; transmission rate is samples per second×bits per sample. Lens power P=1/f and for real converging-lens images 1/f=1/u+1/v using the specified Cartesian convention.
- Calculate magnification from image/object height and v/u; use v=fλ for a wave with f=1/T; calculate noise-limited bit depth from a voltage ratio and distinguish it from b=log₂N, which relates bits to the number of quantisation levels. Become familiar with the supplied H557 Data, Formulae and Relationships booklet: it is provided in examinations, but familiarity is needed to locate and apply the right relationship, data and units accurately.
What to do in an assessment
- Calculate total bits as pixels×bits per pixel and sampling rate above twice the signal frequency; for Vtotal=4.0 V and Vnoise=0.010 V, b=log₂(400)≈8.64, so a whole-bit system can carry at most 8 bits under this limit.
- Apply lens power, thin-lens and magnification equations with the H557 Cartesian convention.
In plain language
A digital image file grows when spatial resolution, colour depth or both increase. Keep the booklet's two logarithm relations straight: b=log₂N counts available levels, whereas b=log₂(Vtotal/Vnoise) sets a noise-limited sample depth.
Self-check
A 1000×800 image stores 8 bits per pixel. How many bits before compression?
Show the answer
1000×800×8=6.4×10⁶ bits.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §3.1.2(a)(i)-(ix); 3.1.2(b)(i)-(iii)
Open revision guidance
What to know
- Current is rate of charge flow I=ΔQ/Δt; p.d. is energy transferred per charge and emf ε is energy supplied per charge. A source with internal resistance r gives terminal voltage V=ε−Ir. For series resistors Rseries=ΣR and the same current gives V1/V2=R1/R2; for parallel branches 1/Rparallel=Σ(1/R), equivalently conductances add, Gparallel=ΣG. In a series combination conductance is the reciprocal of total resistance, 1/Gseries=Σ(1/G).
- Electrical power is P=IV=I²R (also V²/R for an ohmic component); for constant V and I, electrical work W=VIt. An ohmic conductor at fixed temperature has a straight I–V graph through the origin. Learn standard cell, supply, switch, resistor, variable resistor, lamp, diode, thermistor, LDR, ammeter and voltmeter symbols and place ammeters in series and voltmeters in parallel.
- On a resistance/conductance-versus-temperature graph, an ohmic metal's resistance generally rises and conductance falls as it heats; an NTC thermistor's resistance falls and conductance rises. A filament lamp is non-ohmic because heating its filament changes resistance. For a divider, identify which resistor is connected to the output before predicting the voltage change.
What to do in an assessment
- Draw conventional circuit symbols; use I=ΔQ/Δt, V=ε−Ir, the series/parallel rules and P=IV to calculate charge, terminal p.d., equivalent resistance and power with units.
- Plot I against V for an ohmic resistor and a non-ohmic component; sketch R(T) and G(T) for a metal, NTC thermistor and lamp, explaining each curve from temperature-dependent carrier/filament behaviour.
In plain language
A potential divider turns a changing sensor resistance into a changing output voltage.
Self-check
A 2 kΩ resistor has what conductance?
Show the answer
G=1/R=1/(2000 Ω)=5.0×10⁻⁴ S.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §3.1.2(c)(i)-(iv); 3.1.2(d)(i)-(v)
Open revision guidance
What to know
- For an internal-resistance experiment, connect a variable load and measure terminal voltage V for several currents I. Plot V on the vertical axis against I: V=ε−Ir gives y-intercept ε and gradient −r. Example: a gradient of −0.40 V A⁻¹ means r=0.40 Ω; read ε from the fitted intercept.
- For calibration, expose a thermistor to known temperatures measured by a thermometer, or an LDR to known illuminance measured by a light meter; allow the sensor to stabilise, record its electrical output at each known input, plot output against input, repeat over rising and falling values to reveal lag/hysteresis, and interpolate the unknown input from the calibration curve.
- A potential divider has I=Vin/(R1+R2) and V2=Vin R2/(R1+R2) when output is across R2. In a series circuit V1/V2=R1/R2. Power/work relations are P=IV=I²R and W=VIt for steady conditions. For a uniform conductor, conductance G=1/R=σA/L, where σ is conductivity, A cross-sectional area and L length; doubling A doubles G and doubling L halves it.
What to do in an assessment
- Measure length L and cross-section A, use V/I to find resistance R, then calculate ρ=RA/L and σ=1/ρ=L/(RA); equivalently calculate G=σA/L. For example, σ=5.0×10⁷ S m⁻¹, A=2.0×10⁻⁶ m² and L=1.0 m give G=100 S.
- Plot known input against sensor output and use the fitted calibration curve to infer an unknown; report interpolation range, repeats, hysteresis and response time. Determine internal resistance from the negative gradient of a V–I graph. Worked divider: Vin=12 V, Rtop=4.0 kΩ, Rbottom=2.0 kΩ gives Vout=12×2/(4+2)=4.0 V; raising Rbottom raises this output.
In plain language
Calibration relates an instrument's output to a known input; it does not automatically remove hysteresis or response lag.
Self-check
What result follows from this task: A wire has R=4.0 Ω, length 2.0 m, area 1.0×10⁻⁶ m². Find resistivity.
Show the answer
ρ=RA/L=4.0×10⁻⁶/2.0=2.0×10⁻⁶ Ω m.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §3.2(a)(i)-(iv); 3.2(b)(i)-(iv); 3.2(c)(i)-(ii); 3.2(d)(i)-(ii)
Open revision guidance
What to know
- Elastic deformation is recoverable; plastic deformation is permanent, while fracture is failure under load. Direct evidence for particle size/spacing includes scanning-tunnelling-microscope images and Rayleigh's oil-drop experiment. Metals deform through dislocations moving and producing slip; brittle ceramics lack mobile dislocations; polymer response depends on long-chain entanglement and chain unravelling. Stress=F/A, strain=ΔL/L and Young modulus=stress/strain; distinguish strength, stiffness and ductility. Tension pulls a sample apart and compression pushes it together; yield stress marks the onset of permanent deformation. Hardness is resistance to indentation or scratching; toughness is energy absorbed per unit volume before fracture (area under a stress–strain curve).
- For a spring in its Hooke-law region, F=kx. Work done stretching it is the area under the loading force–extension graph: for a straight line from zero, Eelastic=½Fx=½kx². On a curved graph, estimate the area from trapezia. Springs are approximately linear before their limit; rubber bands and polythene can show non-linear loading, hysteresis and permanent extension. Compare force–extension curves for a spring, rubber band and polythene strip and identify extension, recovery and energy-loss evidence.
- Read force-extension and stress-strain graphs through fracture, compare metal/ceramic/polymer structures and determine a metal's Young modulus from controlled extension data. Use the initial straight-line elastic region; fracture stress is the stress at failure, not the Young modulus. At the yield point permanent strain begins; distinguish this yield stress from the maximum fracture stress.
What to do in an assessment
- For springs and polymer samples, add masses in steps, record force F=mg and extension from the unloaded length, then unload to test recovery; plot loading and unloading curves and estimate stored/returned energy from their areas.
- For Young modulus, measure wire diameter at several positions with a micrometer, calculate A=πd²/4, measure original length L, add known forces, record ΔL, plot F against ΔL and obtain E=(L/A)×gradient. For a 1.00 m wire of area 1.00×10⁻⁶ m² extending 0.50 mm under 100 N, stress=1.00×10⁸ Pa, strain=5.00×10⁻⁴ and E=2.00×10¹¹ Pa. To measure fracture stress, load a measured-area specimen in tension or compression in a guarded rig until it fails, record failure force Ffail and calculate σfracture=Ffail/A; 2.0 kN on 20 mm² gives 100 MPa. Identify yield stress at permanent deformation; hardness measures indentation resistance and toughness is the area to fracture on a stress–strain graph.
In plain language
A steep elastic stress-strain graph means greater stiffness, while fracture stress describes failure strength; neither tells you whether the structure deforms by metal slip or polymer-chain unravelling.
Self-check
What result follows from this task: A 1.0 m wire extends 0.50 mm under stress 1.0×10⁸ Pa. Find Young modulus.
Show the answer
Strain=5.0×10⁻⁴; E=2.0×10¹¹ Pa.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §4.1(a)(i)-(viii); 4.1(b)(i)-(ii)
Open revision guidance
What to know
- Standing waves form when counter-propagating waves superpose; nodes and antinodes follow their phase relation. Refraction in the wave model occurs because light changes speed across a boundary while frequency stays fixed, so wavelength changes and the direction bends. Double-slit/grating interference depends on path difference and phase. Electron diffraction by crystalline graphite produces rings as electron de Broglie waves scatter from regularly spaced atomic planes; the ring angles and lattice spacing evidence wave behaviour of matter.
- In the quantum-path model, each possible path contributes an amplitude and phase at the arrival point; add the complex amplitudes first, then probability is proportional to the squared magnitude of the resultant. Amplitudes can reinforce or cancel, so probabilities from separate paths are not simply added before accounting for interference.
- Use phase/phasor and waveform diagrams, apply n=sin i/sin r, calculate path differences, E=hf and de Broglie wavelength λ=h/p. For a distant screen, constructive grating/interference maxima obey nλ=d sin i; at small angle sin i≈i and a double slit gives λ≈xd/D. In the photoelectric effect, work function φ is the minimum energy to release an electron; threshold frequency f₀ satisfies hf₀=φ. Below f₀ no photoelectrons are emitted however intense the light; above it their maximum kinetic energy is hf−φ.
What to do in an assessment
- Explain refraction by tracing wavefronts: the part entering the slower medium first slows first and the direction changes toward the normal; use Snell's law to quantify it. For quantum paths, add amplitude/phase contributions and square the resultant magnitude to compare arrival probabilities.
- Measure interference maxima, convert spacing or angle to path difference, test nλ=d sin i, and calculate photon energy from frequency. Explain the evidence and limitations of wave and particle models.
In plain language
A wave model predicts interference, while photon interactions transfer discrete packets of energy; experiments require both models.
Self-check
What result follows from this task: A photon has frequency 6.0×10¹⁴ Hz. Find its energy.
Show the answer
E=hf≈3.98×10⁻¹⁹ J.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §4.1(c)(i)-(v); 4.1(d)(i)-(vi)
Open revision guidance
What to know
- To find oscilloscope frequency, display several cycles, count horizontal divisions for a period, multiply by the selected time/division, then f=1/T; use the volts/division scale to read amplitude. For refractive index, trace a ray through a transparent block, draw normals, measure i and r with a protractor, calculate n=sin i/sin r, repeat over angles and average.
- For two-source superposition, drive two coherent string or sound sources at the same frequency, vary path difference and map maxima/minima; for microwaves or light, align coherent sources and detector/screen and record intensity versus position. For a resonance tube, vary air-column length with a fixed-frequency tuning fork; adjacent resonances differ by λ/2, then v=fλ.
- For double slit, measure slit separation d, screen distance D and fringe spacing x across several fringes, use λ=xd/D; for a grating, measure angle of order n and use nλ=d sin i. OCR also requires standing-wave wavelength measurements and Planck-constant determination.
What to do in an assessment
- On an oscilloscope find T=(horizontal divisions per cycle)×(time/division), then f=1/T; read amplitude from vertical divisions×volts/division. For a block, measure i and r and calculate n; repeat and average.
- Use coherent sources to map superposition maxima/minima. In a resonance tube, measure two adjacent resonance lengths, take λ=2ΔL and calculate sound speed v=fλ. For a distant double slit use λ=xd/D; for a grating use nλ=d sin i, converting degree angles to radians before small-angle approximations. For LEDs, measure threshold V for several frequencies and plot photon energy eV against f; slope in joules per hertz is h.
In plain language
Practical methods test the predicted relationships—for example, fringe spacing varies with wavelength and screen distance.
Self-check
How can a frequency-versus-photon-energy graph determine Planck's constant?
Show the answer
From E=hf, the gradient of E against f is h (after energy is expressed in joules).
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §4.2(a)(i)-(ix); 4.2(b)(i)-(iii)
Open revision guidance
What to know
- For constant acceleration, use v=u+at, s=ut+½at², v²=u²+2as and average velocity=(u+v)/2, with signed quantities and consistent directions. Momentum p=mv; impulse J=FΔt=Δp, and equal/opposite interaction impulses express Newton's third law. Work W=Fs cosθ; power is energy per time and P=Fv when force is parallel to velocity. Isolated systems conserve total momentum and energy.
- Vectors represent displacement, velocity, acceleration and force. Perpendicular motion components evolve independently. Read slope/area on motion graphs; resolve vectors and calculate p, force, work, kinetic and gravitational energy.
What to do in an assessment
- For each constant-acceleration problem identify u,v,a,t,s, choose one of the four equations, rearrange first and check units. For an impulse question, calculate the area under an F–t graph or use Δp; compare interaction impulses as equal and opposite.
- Calculate P=Fv for a force parallel to motion (or power=work/time); state the system boundary before invoking conservation laws and use signed momentum.
In plain language
The same interaction can change an object's momentum while total momentum of an isolated system remains fixed.
Self-check
A 0.50 kg object moving at 4.0 m s⁻¹ stops. What is its initial momentum?
Show the answer
p=mv=2.0 kg m s⁻¹.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §4.2(c)(i)-(xi); 4.2(d)(i)-(iii)
Open revision guidance
What to know
- A discrete-time model advances in steps Δt: calculate acceleration a=Fresultant/m, update velocity vnew=vold+aΔt, then position xnew=xold+voldΔt (or use mean velocity for the step); plot velocity and position vectors at each step. With zero resultant force velocity remains constant; with constant force velocity changes linearly.
- For trapdoor/electromagnet free fall, hold a steel ball at an electromagnet above a trapdoor, switch off current to release and start timing, then stop the timer at impact; measure drop height and repeat. Alternatively use light gates/video/data logger, fit s–t or v–t data and find g from the gradient. Practical contexts also include trolley/air-track collisions and terminal velocity.
What to do in an assessment
- For trolley collisions, obtain velocities immediately before/after using two light gates, ticker tape, video or data logger; calculate total signed momentum before and after and compare within uncertainty.
- For electromagnet/trapdoor free fall measure h and t repeatedly, use h=½gt² or a fitted motion graph, and discuss release delay and air resistance. For terminal velocity, track a ball bearing falling through liquid: estimate speed over equal intervals until successive speeds become constant.
In plain language
A practical collision result tests whether momentum remains conserved within measurement uncertainty.
Self-check
What result follows from this task: A 0.20 kg trolley at 3.0 m s⁻¹ couples to a stationary 0.40 kg trolley. Find their shared speed.
Show the answer
0.20×3.0=(0.60)v, so v=1.0 m s⁻¹.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §5.1.1(a)(i)-(viii); 5.1.1(b)(i)-(viii)
Open revision guidance
What to know
- Capacitance C=Q/V and capacitor energy E=½QV=½CV². During discharge Q=Q₀e^(−t/RC), V=V₀e^(−t/RC) and current magnitude I=(V₀/R)e^(−t/RC); during charging from supply Vs, Q=CVs(1−e^(−t/RC)), V=Vs(1−e^(−t/RC)) and I=(Vs/R)e^(−t/RC). Current is positive into the capacitor while charging, so discharge current has the opposite sign in that convention. A capacitor's Q–V graph has area equal to stored energy.
- Radioactive decay is random for an individual nucleus but has a fixed probability per unit time for the population: dN/dt=−λN, N=N₀e^(−λt), activity A=−dN/dt=λN and T½=ln2/λ. In SHM, a=−ω²x, ω=2πf, and x=A sin(ωt) or A cos(ωt); velocity and acceleration are phase-shifted.
- For a mass-spring oscillator T=2π√(m/k), for a simple pendulum T=2π√(L/g). The spring force magnitude is F=kx and stored energy is ½kx²; oscillator energy Etotal=½mv²+½kx² remains constant in the ideal undamped model. Damping reduces amplitude; a driven oscillator's amplitude peaks near resonance.
What to do in an assessment
- From a Q–V graph calculate stored energy as its area; for a triangle from (0,0), E=½QV. Plot ln Q against t to obtain slope −1/RC or ln N against t to obtain slope −λ, then infer τ or T½.
- Sketch x=A sinωt, v=Aω cosωt and a=−Aω² sinωt; mark their phase and show energy exchanging between ½kx² and ½mv². Plot resonator amplitude against driving frequency and identify damping/resonance.
In plain language
A mathematical model shows a shared exponential pattern but does not make electrical discharge and nuclear decay the same physical mechanism.
Self-check
A capacitor voltage halves every 4 s. What fraction remains after 12 s?
Show the answer
Three half-times have passed, so 1/8 remains.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §5.1.1(c)(i)-(xi); 5.1.1(d)(i)-(iv)
Open revision guidance
What to know
- Calculate A=λN and T½=ln2/λ from repeated count-rate data after subtracting background; a fitted ln(activity)-time gradient is −λ. For a capacitor with τ=RC, discharge gives Q=Q₀e^(−t/τ), V=V₀e^(−t/τ), |I|=(V₀/R)e^(−t/τ); charging from Vs gives Q=CVs(1−e^(−t/τ)), V=Vs(1−e^(−t/τ)), I=(Vs/R)e^(−t/τ), with charge current defined into the capacitor. Energy E=½QV=½CV².
- Solve a rate model numerically by small steps: for dQ/dt=−Q/RC, update Qnew=Qold−(Qold/RC)Δt; for dN/dt=−λN use Nnew=Nold−λNoldΔt. For second-order SHM, at each step evaluate aₙ=−ω²xₙ, then update vₙ₊₁=vₙ+aₙΔt and xₙ₊₁=xₙ+vₙΔt; tabulate x,v,a and compare the resulting motion/period with a sinusoid. Halve Δt and compare the trajectories to test convergence, or plot derivative against the dependent variable and infer the constant from the gradient.
- For mass-spring motion T=2π√(m/k); for a pendulum T=2π√(L/g). Use F=kx, Eelastic=½kx², x=A sin(2πft) or A cos(2πft), a=−(2πf)²x and Etotal=½mv²+½kx².
What to do in an assessment
- Calculate τ=RC; from Q or V decay fit ln(signal) against t, read λ from the negative gradient and find T½=ln2/λ. For numerical rate equations tabulate each state, evaluate the rate at the current value and step forward by Δt; check stability by reducing Δt.
- Measure many periods for several masses/lengths, plot T² against m for a spring or T² against L for a pendulum, and compare slope with the model; sketch x,v,a phases and measure amplitude versus driving frequency for damped/forced oscillations. To iterate SHM, start from x₀,v₀, evaluate a=−ω²x at each step, update v then x over Δt, plot the trajectory and repeat with smaller Δt to check that it converges.
In plain language
The equations are linked through patterns such as exponential change or energy exchange, while the systems retain different causes.
Self-check
What result follows from this task: A 47 μF capacitor is connected to a 100 kΩ resistor. Find τ.
Show the answer
τ=RC=4.7 s.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §5.1.2(a)(i)-(v); 5.1.2(b)(i)-(iv); 5.1.2(c)(i)-(vi)
Open revision guidance
What to know
- This section is gravity, not radar or relativity. In a uniform gravitational field, ΔEgrav=mgΔh; work is ΔE=FΔs, with zero work when force is perpendicular to displacement or motion follows an equipotential. For a spherical mass M modelled as a point mass at its centre, Fgrav=−GMm/r², g=−GM/r², Egrav=−GMm/r and Vgrav=Egrav/m=−GM/r. The negative signs indicate an attractive field and zero potential at infinity.
- Angular velocity ω is measured in rad s⁻¹; circular motion has a=v²/r=rω² and F=mv²/r=mrω². In a circular gravitational orbit, gravity supplies centripetal force. Field/potential graphs encode derivatives and areas: the gradient of gravitational potential gives field strength, the gradient of potential energy gives force, and the area under field-versus-distance or force-versus-distance graphs gives the corresponding potential or energy change with the stated sign convention.
What to do in an assessment
- Calculate energy changes in a uniform field and for a point mass; equate GMm/r²=mv²/r to derive v=√(GM/r) and T=2π√(r³/GM) for a circular orbit.
- Sketch radial field lines and equipotentials, label r from the central mass, and read slope/area meaning from field, potential, force and potential-energy graphs.
In plain language
Outside a spherical body, its field is modelled as if its mass were concentrated at its centre; orbit speed and period follow by balancing gravity with centripetal force.
Self-check
A satellite orbits a spherical planet of mass 6.0×10²⁴ kg at radius 8.0×10⁶ m. What are its circular speed and gravitational potential?
Show the answer
v=√(GM/r)=√[(6.67×10⁻¹¹)(6.0×10²⁴)/(8.0×10⁶)]≈7.1×10³ m s⁻¹; Vgrav=−GM/r≈−5.0×10⁷ J kg⁻¹.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §5.1.3(a)(i)-(iv); 5.1.3(b)(i); 5.1.3(c)(i)-(ii)
Open revision guidance
What to know
- Radar ranging within the Solar System defines distance through light-travel time using invariance of c; for round-trip delay Δt, range d=cΔt/2. For a reflected radar signal from a target moving much slower than c, the round-trip Doppler shift is approximately |Δf|/f≈2|v|/c; the echo shifts lower for recession and higher for approach, so v≈(c/2)(Δf/f) with a signed direction convention.
- Relativistic time dilation uses γ=1/√(1−v²/c²): a moving clock's interval is Δt=γΔτ, where Δτ is its proper time. Hot-Big-Bang evidence includes cosmological redshift/Hubble's law and the CMB. Redshift z=(λobserved−λemitted)/λemitted; for small z, recession speed v≈cz and Hubble's law is v≈H₀d. A distance d also gives a light-travel look-back time t≈d/c; 1/H₀ is an order-of-magnitude expansion timescale, not an exact age without a cosmological model.
- Estimate distances with radar light-time or stellar parallax d(pc)=1/p(arcsec), and ages from the corresponding light-travel time or stated model data. Interpret a logarithmic axis by comparing powers of ten: a separation of two decades is a factor 100, not an additive difference of 2. Use logarithmic scales for distance, size, mass, energy, power and brightness.
What to do in an assessment
- For an echo delay of 2.0 μs, range d=cΔt/2=(3.00×10⁸)(2.0×10⁻⁶)/2=300 m. If a 1.00 GHz echo is 200 Hz lower, recession speed is about c(200)/(2×1.00×10⁹)=30 m s⁻¹. Calculate γ and the dilated interval; at v=0.60c, γ=1.25, so a 4.0-year proper interval is 5.0 years in the other stated frame.
- For parallax p=0.10 arcsec, d=10 pc and light-travel time is about 32.6 years (1 pc≈3.26 light years). Interpret a log-scale tick change of 2 as ×100. Use z≈v/c and v=H₀d at small redshift; a 2.7 K CMB blackbody supports the hot early-universe model. State model assumptions rather than presenting inferred age as direct observation.
In plain language
A spectral redshift and the CMB are measured evidence; an expanding hot-Big-Bang history is a model that explains those observations.
Self-check
A radar echo at 1.0 GHz returns 200 Hz lower than transmitted. Estimate recession speed. A star has parallax 0.10 arcsec; estimate its distance and light-travel time.
Show the answer
v≈(c/2)(200/1.0×10⁹)=30 m s⁻¹ away. d=1/p=10 pc≈32.6 light-years, so its light-travel time is about 32.6 years.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §5.2.1(a)(i)-(vi); 5.2.1(b)(i)-(iii); 5.2.1(c)(i)-(iii); 5.2.1(d)(i)-(iii)
Open revision guidance
What to know
- Heating transfers energy and changes temperature according to Q=mcΔT, where c is specific thermal capacity. In kinetic theory pV=⅓N m⟨c²⟩=⅓N m c_rms²; comparing with pV=NkT gives ½m c_rms²=3/2 kT and c_rms=√(3kT/m). RMS speed is √(mean of squared speeds), not the arithmetic mean speed. For a monatomic ideal gas, internal energy U=3/2 NkT=½N m c_rms²; internal energy is microscopic energy, distinct from bulk kinetic energy.
- Gas pressure is momentum transfer: each wall collision changes molecular momentum Δp and the net force is the momentum change per time. Impulse on a particle is FΔt=Δp; on an F–t graph, signed area is impulse. Ideal-gas assumptions: particle volume negligible, collisions elastic and intermolecular forces negligible except during collisions. For a random walk of N independent steps, typical net displacement grows as √N, not N. To investigate the pressure–volume relation, trap a fixed gas sample at constant temperature, vary its volume, read absolute pressure from a pressure gauge or differential-pressure monitor and log paired p,V readings; plot p against 1/V to test pV=constant.
What to do in an assessment
- Use pV=nRT or pV=NkT with kelvin and consistent particle/mole quantities. Example: 0.20 kg with c=900 J kg⁻¹ K⁻¹ heated by 5.0 K receives Q=900 J. For 2.0 mol at 300 K and 0.050 m³, p=nRT/V≈1.0×10⁵ Pa.
- A gas has N=2.0×10²³ molecules, molecular mass 4.65×10⁻²⁶ kg and c_rms=500 m s⁻¹: pV=⅓Nmc_rms²≈3.1×10³ J. On an F–t graph, calculate impulse from trapezium area; a 2.0 N average force acting 0.10 s gives 0.20 N s. For 100 random steps, the characteristic net displacement is 10 step lengths.
In plain language
Gas molecules do not all travel at one speed; temperature sets a statistical average.
Self-check
At constant N and V, what happens to pressure when kelvin temperature doubles?
Show the answer
It doubles under the ideal-gas model.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §5.2.2(a)(i)-(ii); 5.2.2(b)(i); 5.2.2(c)(i)-(ii)
Open revision guidance
What to know
- For states separated by energy ΔE, the classical population ratio is proportional to exp(−ΔE/kT); compare ΔE with kT before calculating. At fixed T, a plot of Boltzmann factor exp(−E/kT) against energy falls exponentially; larger T gives a less steep curve. At fixed positive ΔE, the factor rises with T.
- In an activation-energy process only particles with sufficient energy contribute effectively: raising temperature increases that fraction and changes rates/flows. Apply qualitatively to melting/evaporation, thermionic emission, ionisation, increasing semiconductor conduction, and temperature-dependent viscous flow (typically a liquid flows more readily as viscosity falls when warmed). Do not confuse a population/activation trend with a new energy level.
What to do in an assessment
- For ΔE=0.20 eV at kT=0.050 eV, the relative factor is exp(−4)=0.018; if kT doubles to 0.10 eV it becomes exp(−2)=0.135. On a graph against energy, draw a decreasing exponential and show the higher-temperature curve falling more slowly.
- Explain the effect of increased T separately for each example: more electrons escape a heated cathode (thermionic emission), more semiconductor carriers are available, and thermal energy can drive phase change/ionisation; describe the corresponding change in viscous flow without assuming all materials behave identically.
In plain language
When thermal energy is small compared with a level gap, the higher-energy state is much less populated.
Self-check
What happens to exp(−ΔE/kT) as T increases for fixed positive ΔE?
Show the answer
The exponent becomes less negative and the ratio increases.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §6.1.1(a)(i)-(iv); 6.1.1(b)(i)-(iii); 6.1.1(c)(i)-(iv); 6.1.1(d)(i)-(iii)
Open revision guidance
What to know
- A transformer uses changing magnetic flux linking windings; a dynamo induces emf when flux linkage changes. Faraday's law ε=−d(NΦ)/dt and Lenz's law set magnitude and opposing direction. Flux lines form continuous closed paths: they do not start/end in the core, and their density represents B.
- For a linked magnetic circuit, magnetomotive force NI drives flux Φ=permeance×NI, analogous to current=conductance×potential difference. Larger core cross-section raises permeance; a longer magnetic path lowers it; high-permeability iron guides flux, while an air gap has low permeability and adds high reluctance, reducing flux. Increasing machine dimensions can allow more linked flux, but longer windings also alter resistance and current.
- Current in a uniform magnetic field feels F=ILB when perpendicular. For an ideal transformer Vs/Vp=Ns/Np and Is/Ip=Np/Ns; output voltage rises as turns ratio rises while current ratio reverses. An actual transformer investigation uses an AC primary supply and meters to measure primary/secondary voltage and current while turns ratio and secondary load are varied.
What to do in an assessment
- Sketch a closed magnetic flux path through core and air gap; compare line spacing, label flux continuity and explain why inserting iron or widening the gap changes permeance/flux.
- For a falling-magnet demonstration, connect a coil to a voltage sensor/data logger, release a bar magnet through it and record the emf-time pulse; reverse the magnet or motion to reverse polarity, and vary speed/turns to compare peak emf. For B, pass a rigid horizontal current carrier through a magnet gap on a digital balance, measure current I and added balance force F=Δmg, then calculate B=F/(IL) or plot F against I. To investigate a transformer, connect its primary to a low-voltage AC supply and meters, measure primary and secondary rms voltage/current, vary turns ratio and then secondary load, and compare Vₛ/Vₚ with Nₛ/Nₚ; stay within equipment ratings and never connect a teaching transformer directly to mains.
In plain language
A transformer transfers energy through changing linked flux, not direct electrical connection between its coils.
Self-check
What result follows from this task: An ideal transformer has 1000 primary turns and 100 secondary turns; primary voltage is 240 V. Find secondary voltage.
Show the answer
Vs/Vp=Ns/Np, so Vs=24 V.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §6.1.2(a)(i)-(vi); 6.1.2(b)(i)-(iv); 6.1.2(c)(i)-(iv)
Open revision guidance
What to know
- A point charge Q exerts radial Coulomb force F=kQq/r² on q and creates field E=F/q=kQ/r²; potential V=kQ/r and potential energy U=qV=kQq/r, with signs set by charges. In a uniform field E=V/d in magnitude; for a radial field E=−dV/dr. A moving charge in perpendicular uniform B experiences F=qvB. Millikan's oil-drop measurements show charge occurs in integer multiples of e.
- The signed area under E-versus-r is −ΔV, and area under force-versus-r is ΔU; conversely field strength E is the negative gradient of potential and force is the negative gradient of potential energy. Equipotentials are perpendicular to field lines. Compare electric and gravitational fields, noting mass is always positive whereas charge may be either sign.
What to do in an assessment
- For a source Q and test charge q at radius r calculate F=kQq/r², V=kQ/r and U=kQq/r; show signed radial directions. From V(r), differentiate to get E=−dV/dr; from an E–r graph, use signed area to find potential change.
- For a force–distance graph use area for work/ΔU; for U(r), gradient gives −F. Label equipotential contours perpendicular to field lines and compare with gravitational field/potential graphs.
In plain language
A positive and negative charge in the same electric field feel opposite forces.
Self-check
What result follows from this task: A 2.0 μC charge moves through 5.0 V. Find its potential-energy change magnitude.
Show the answer
ΔE=qV=1.0×10⁻⁵ J.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §6.2.1(a)(i)-(vii); 6.2.1(b)(i)-(iii); 6.2.1(c)(i)-(iv)
Open revision guidance
What to know
- Accelerators produce energetic beams; scattering angles and energy loss reveal a small massive nucleus. Atomic energy levels are discrete; in a simple standing-wave model an allowed electron orbit fits an integer number of de Broglie wavelengths around its circumference, 2πr=nλ. Protons uud and neutrons udd are made from quarks; gluons mediate the strong interaction.
- Balance nuclear/particle equations by conserving nucleon number, electric charge and lepton number as well as energy. Example β⁻ decay n→p+e⁻+anti-νe has charge 0=+1−1 and lepton number 0=+1−1. Use the full particle vocabulary: proton/neutron are nucleons and hadrons, electron/positron/neutrino are leptons, and each antiparticle has opposite conserved quantum numbers.
- For charged-particle paths in B, use qvB=mv²/r to find r=mv/(|q|B). A potential difference changes kinetic energy by ΔEk=qΔV and electric potential energy by ΔU=qΔV; for Coulomb motion ΔU=kqQ(1/r₂−1/r₁), with ΔEk=−ΔU in an isolated conservative interaction. At relativistic speed use Erest=mc² and Etotal=γErest.
What to do in an assessment
- Sketch incoming and outgoing alpha-particle paths past a compact nucleus; use rare large-angle deflections to infer that positive charge and most mass are concentrated in a small region. Draw electron standing waves with 2πr=nλ and explain why only discrete radii/energies are allowed in this simple model.
- Check charge, nucleon number and lepton number on both sides of a reaction before solving for a missing particle. Example: a proton crosses 200 V, so ΔEk=e(200 V)=3.2×10⁻¹⁷ J; use qvB=mv²/r if its path curves in B.
In plain language
Scattering reveals interior structure by observing how projectiles are deflected rather than directly seeing a nucleus.
Self-check
What rest energy corresponds to a 1.0 kg mass?
Show the answer
E=mc²=9.0×10¹⁶ J.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §6.2.2(a)(i)-(iii); 6.2.2(b)(i)-(ii); 6.2.2(c)(i)-(iv); 6.2.2(d)(i)-(ii)
Open revision guidance
What to know
- Ionising radiation can damage living tissue by ionising molecules/DNA, leading to cell death or mutation; consequence depends on radiation, absorbed energy, tissue and exposure. Absorbed dose D=energy deposited/mass in gray (J kg⁻¹); effective/equivalent dose is D×radiation weighting factor in sievert, a risk-weighted quantity.
- Nuclei are specified by proton number Z, nucleon number A and neutron number A−Z; isotopes share Z but differ in neutron number. The atomic mass unit u is 1/12 the mass of a carbon-12 atom. Binding energy per nucleon peaks near iron/nickel on a plot against A; light nuclei release energy by fusion toward the peak, heavy nuclei by fission toward it. The Nuclear Valley maps stable nuclides among proton/neutron numbers.
- Fission of a heavy nucleus can release neutrons and sustain a chain reaction; controlled fission power uses fuel, moderator/control systems and heat transfer. Fusion of light nuclei powers stars but requires extreme temperature/confinement. Evaluate benefits, waste, accident risk, radiation dose and environmental/social trade-offs.
What to do in an assessment
- Sketch binding energy per nucleon against A with a peak near iron/nickel; explain why both light-nucleus fusion and heavy-nucleus fission can release energy. Draw a Nuclear Valley map and identify isotopes by same Z but different A.
- Calculate activity A=λN and T½=ln2/λ, dose D=E/m in Gy and weighted dose in Sv, and nuclear energy change ΔE=Δmc². Compare radiation risks using dose and biological weighting, not activity alone; background-correct detector readings and use shielding/distance under supervised safety procedures.
In plain language
Hazard depends on radiation, exposure, dose and context; activity alone is not an individual’s effective dose.
Self-check
A 4.0 mGy absorbed dose has radiation weighting factor 20. What effective dose?
Show the answer
Equivalent/effective dose=4.0×20=80 mSv, under the simplified specified weighting.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §5e M0-M4; 5d HSW1-HSW12
Open revision guidance
What to know
- M0 arithmetic—M0.1 identify units and convert prefixes (3.0 cm³=3.0×10⁻⁶ m³); M0.2 use decimal/standard form (c=3.00×10⁸ m s⁻¹); M0.3 calculate ratios, fractions, percentages and percentage uncertainty; M0.4 estimate the effect of changing a measurable parameter before calculation; M0.5 use calculator powers, exponentials and logarithms to solve equations such as N=N₀e^(−λt); M0.6 calculate sin, cos or tan in the stated degree/radian mode and check calculator mode.
- M1 data—M1.1 report significant figures no more precise than the least accurate input; M1.2 calculate the arithmetic mean of repeats; M1.3 interpret decay probability for individual nuclei and populations; M1.4 estimate order of magnitude by powers of ten; M1.5 propagate uncertainty: for sums/differences add absolute uncertainties; for products/quotients/powers combine fractional or percentage contributions using the stated rule, or test upper/lower extremes. Example: two lengths 10.0±0.1 and 5.0±0.1 cm summed give 15.0±0.2 cm.
- M2 algebra—M2.1 interpret symbols and rates, e.g. F=Δp/Δt means momentum change per time; M2.2 rearrange linear/non-linear equations (from E=mc² obtain m=E/c²); M2.3 substitute values with coherent SI units (p=mv); M2.4 solve algebraic/quadratic equations (choose the physically valid root of s=ut+½at²); M2.5 interpret logarithmic scales spanning decades.
- M3 graphs—M3.1 translate between graph, numerical and algebraic forms; M3.2 plot paired data with labels, units and sensible scale; M3.3 identify y=mx+c; M3.4 find gradient/intercept; M3.5 use a straight-line gradient as rate; M3.6 draw a tangent for local rate; M3.7 distinguish tangent (instantaneous) from interval (average) gradient; M3.8 estimate area by counting squares/trapezia and explain its physical meaning; M3.9 solve rate-change models graphically or by spreadsheet iteration without formal calculus; M3.10 interpret log axes; M3.11 linearise/test exponential and power laws using logarithms; M3.12 sketch y=k/x, kx², k/x², kx, sin x, cos x, e^±x, sin²x and cos²x.
- M3 worked method: for a curved displacement-time plot draw a tangent, select widely separated points on it and compute Δs/Δt for instantaneous velocity. To find τ from capacitor decay, plot ln(V/V₀) against t; gradient=−1/τ, so a gradient −0.25 s⁻¹ gives τ=4.0 s. A Q–V area gives capacitor energy; use trapezia if data are discrete.
- M4 geometry/trigonometry—M4.1 use angles in regular 2D/3D structures; M4.2 represent 2D/3D objects and draw force diagrams; M4.3 calculate triangle/circle areas, circumferences, block/cylinder/sphere areas and volumes; M4.4 use Pythagoras and triangle angle sum; M4.5 apply sin/cos/tan to resolve vectors; M4.6 use sin i≈i, tan i≈i, cos i≈1 only for small i in radians (a 0.050 rad angle has sin i≈0.050); M4.7 convert θ(rad)=θ(deg)π/180, e.g. 2.0°=0.0349 rad.
- HSW1 explain with theories/models; HSW2 pose questions, define problems and present arguments; HSW3 select methods/ICT; HSW4 investigate with risk management; HSW5 analyse evidence, correlation and causation; HSW6 evaluate method/data and conflicting evidence; HSW7 explain development of knowledge; HSW8 communicate for audience and purpose; HSW9 weigh benefits/risks; HSW10 evaluate ethical issues; HSW11 consider peer review and integrity; HSW12 evaluate science informing social decisions.
- Graph method: draw a tangent at the specified point on a curve, choose two well-separated points on the tangent, then find Δy/Δx for the instantaneous gradient. To determine an RC time constant, plot ln V against t: ln(V/V₀)=−t/RC, so gradient=−1/RC and τ=−1/gradient. A tangent on a curved graph is not the same as average change over an interval.
What to do in an assessment
- For calculations use the relevant code skill: convert units first, estimate scale, rearrange, substitute with units, use the correct trig/log mode, propagate uncertainty and round only to justified significant figures.
- For graphs label variables/units, plot accurately, choose best-fit line or tangent, calculate slope/intercept/area with units, interpret it using the physical model and state spread/uncertainty. For rate models, make a table of successive Δt steps, evaluate the rate, update the variable and halve Δt to check stability.
- For logarithmic data identify the axis base and decade spacing; linearise an exponential by plotting ln y against x and a power law by plotting ln y against ln x. Explain the physical meaning of slope/intercept, rather than reporting a fitted line alone.
In plain language
The same data can support a model only when uncertainty and alternative explanations are considered.
Self-check
A graph of ln(V/V₀) against time has gradient −0.25 s⁻¹. Find τ, and state when to use a tangent.
Show the answer
Gradient=−1/τ, so τ=−1/(−0.25)=4.0 s. Use a tangent to estimate instantaneous rate on a curved graph; use the straight-line gradient for the transformed exponential.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §5d HSW1-HSW12
Open revision guidance
What to know
- HSW1 use theories/models to explain: predict a result from a model, compare it with data and state where the model works. HSW2 pose a testable scientific question, define the problem and make a reasoned argument. HSW3 choose appropriate method and ICT, e.g. sensor/logger versus stopwatch based on response time.
- HSW4 carry out safe investigations: identify hazards, assess risk, choose controls and follow a repeatable procedure. HSW5 analyse data, identify trends/correlation and do not claim causation unless alternative variables are controlled. HSW6 evaluate method/data, quantify limitations and reconcile or explain conflicting evidence.
- HSW7 explain that scientific knowledge develops as measurements, technologies and models change. HSW8 communicate for a defined audience using precise terms, labelled units and a clear evidence-based structure.
- HSW9 weigh scientific applications' benefits against risks and uncertainty. HSW10 assess ethical consequences for people, other organisms and environment. HSW11 explain how peer review, independent repetition and scientific integrity validate knowledge. HSW12 evaluate how society uses scientific evidence in policy or personal decisions, including uncertainty and trade-offs.
What to do in an assessment
- Build a claim–evidence–reasoning response: state the question and model; identify measured evidence and uncertainty; separate observation from inference; test an alternative explanation; evaluate method, repeatability and conflicting results; then communicate the conclusion for its audience.
- For an application, identify beneficiaries and affected groups, quantify plausible benefits/risks where evidence permits, discuss ethical/environmental effects, and explain which scientific evidence informs a decision without presenting science as the sole value judgement.
In plain language
A strong scientific explanation says what the evidence shows, how a model explains it, how certain that conclusion is, and what remains open to question.
Self-check
Two laboratories obtain different values for a material constant. Name a suitable HSW approach before choosing one value.
Show the answer
Compare methods, calibration, uncertainty and sample conditions; repeat independently and consider peer review. HSW5/6/11 require evaluating evidence and resolving the disagreement, not selecting the preferred result without reasons.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §2a; 3a; 3b; 3i; 3j
Open revision guidance
What to know
- H557/01 is 110 marks/2 h 15 min: Section A multiple choice (~30), B short structured/problem-solving/calculation/practical (~20), C short-answer plus extended response (~60). H557/02 is 100 marks/2 h 15 min: A short structured/problem-solving/calculation/practical (~30), B those styles plus extended response (~45), C short and extended responses based on the Advance Notice (~25). /03 is 60 marks/1 h 30 min: A short structured/problem-solving/calculation/practical (~40), B a longer structured practical/problem-solving/calculation/extended-response data-analysis question (~20).
- All three written papers draw content from Modules 1–6, include synoptic assessment, extended responses and stretch/challenge questions. AO1 is knowledge/understanding of ideas, processes, techniques and procedures; AO2 applies them theoretically, practically and to qualitative/quantitative data; AO3 analyses, interprets and evaluates information/evidence to make judgements, conclusions and refine practical designs.
- A-level AO ranges are AO1 30–35%, AO2 40–44%, AO3 25–28%. Component AO ranges are /01 AO1 15–17%, AO2 16–17%, AO3 8–9%; /02 11–12%, 15–17%, 10–11%; /03 4–6%, 9–10%, 7–8%. The separately reported /04 endorsement has no AO contribution to the overall grade.
- Synoptic assessment explicitly connects knowledge across the course: for example, use mechanics and circuit measurement together to plan an investigation, or apply field, energy and particle models to interpret new data. OCR converts each written component mark according to its weighting and sums the three weighted marks; the total is compared with that series/entry-option qualification boundary. The /04 result is not added. Boundaries vary by series, so never invent a fixed grade cutoff.
- For example, if the scaled contributions are 32/41 from /01, 27/37 from /02 and 17/22 from /03, the total weighted mark is 76/100. This arithmetic illustrates adding weighted components only; it does not predict a grade without the official boundary for that series.
What to do in an assessment
- Plan /01 across MCQ, short-answer and extended-response sections; for /03 practise short experimental-method items followed by a longer data-analysis response. On /02 allocate time to A/B and the article-based C section rather than over-investing in the Advance Notice.
- Identify whether a task assesses AO1 recall, AO2 application, or AO3 evaluation, while recognising a question can integrate them. For a synoptic response state the connecting principles and show how evidence links them. Add only the weighted marks from /01–/03 and use the official entry-option boundary; report /04 separately.
In plain language
The final teaching and final assessment dates are different: the award still has a 2027 cohort.
Self-check
A learner receives scaled weighted contributions of 32, 27 and 17 marks from /01, /02 and /03. What is the total weighted mark, and does the /04 endorsement add to it?
Show the answer
32+27+17=76 total weighted marks. No: /04 is separately reported and not included in the overall A-level grade; compare 76 with the official series/entry-option boundary.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §5c Data, Formulae and Relationships; §5f Advance Notice for H557/02
Open revision guidance
What to know
- The Data, Formulae and Relationships booklet is supplied in H557 examinations, so learn to find the needed relation and check what each symbol, unit and condition means. For example, the booklet gives the noise-limited sample-depth relation b=log₂(Vtotal/Vnoise), distinct from b=log₂N for N quantisation levels.
- The pre-release Advance Notice for /02 consists of scientific article(s) linked to H557; related questions carry 20–25 marks. Read the article before the exam and apply full-course physics. The exam paper includes a fresh copy as an insert; candidates may not take the pre-release copy into the room.
- The article is only part of /02. Questions require scientific literacy: interpret the article, relate claims and data to physics, evaluate evidence/limitations and manage time across the rest of the paper.
What to do in an assessment
- Practise locating a formula in the booklet, defining its symbols, converting to consistent SI units, rearranging and checking the model assumptions before substitution.
- When OCR issues the cohort article, annotate its claims, quantities, graphs, evidence and uncertainty; investigate context with reliable sources and practise applying H557 knowledge rather than trying to predict unseen questions.
- In the exam, cite details from the fresh insert, show the physics reasoning and limitations, and retain time for non-article questions.
In plain language
Supplied material helps you reason; it does not do the reasoning for you.
Self-check
Can the pre-release article be taken into the exam, and how many marks are linked to it?
Show the answer
No. H557/02 includes a fresh copy as an insert; Advance Notice questions are worth 20–25 marks.
- Core
Scope: Core · OCR H557 Specification v2.9 (March 2026), §1.2; §5h Table 1 PAG1-PAG12 and CPAC
Open revision guidance
What to know
- PAG1 motion (free fall): use an analogue metre rule to measure drop height, interpolate scale readings, align the apparatus with a set square/plumb line, release consistently, time with a stopwatch or light gates and repeat; use a data logger/sensor or video to capture motion, then obtain g=2s/t² or the gradient of s against t². PAG2 materials: zero a vernier/digital caliper or micrometer, measure wire diameter at several orientations, measure L, hang known masses, record extension in the elastic region, plot F–ΔL and calculate E=(L/A)gradient.
- PAG3 electrical properties: construct a safe DC I–V circuit from a diagram, place the ammeter in series and voltmeter in parallel, select multimeter ranges, record I and V, then measure L and wire cross-section and calculate ρ=RA/L. PAG4 electrical circuits: assemble and check a divider (including polarity for diode/sensor), measure Vin and output for known resistor or thermistor/LDR inputs, vary the independent input, record repeat output values and plot/calibrate response; for a simple divider, Vout=Vin Rlower/(Rupper+Rlower).
- PAG5 waves: use a signal generator and oscilloscope to read volts/division and time-base; generate two coherent sound sources with speakers or two wave sources, map maxima/minima against position and infer wavelength, or measure double-slit fringe spacing w and screen distance L and calculate λ=wd/L; for a grating use d sin θ=nλ. PAG6 quantum: wire an LED with correct polarity and current limiting, measure threshold voltage for LEDs of known frequency, convert energy eV to joules and plot photon energy E against frequency f; E=hf+work-function contribution, so gradient gives h.
- PAG7 radiation: under supervised risk controls measure background first, place detector at fixed distance, insert absorber thickness/materials systematically, repeat counts for equal time and subtract background; use shielding and never handle sources outside authorised controls. PAG8 gases: use analogue scales and interpolation for pressure, volume and temperature, control variables, collect pressure-versus-temperature data at fixed volume (P∝T in kelvin) and extrapolate the straight-line trend to zero pressure for absolute zero.
- PAG9 capacitors: check an RC circuit, select safe voltage/current/time ranges, charge/discharge and log V or I at known times; plot ln V or ln I against t, obtain gradient −1/RC and τ=−1/gradient. PAG10 SHM: use analogue distance measurement, a fiducial marker/plumb alignment, time many periods digitally, repeat across masses or lengths, calculate T and graph T² against m (spring: T=2π√(m/k)) or L (pendulum: T=2π√(L/g)); use a logger/software where useful and observe damping/forced response.
- PAG11 specific heat: insulate a metal block or liquid, measure mass and starting temperature, immerse heater/thermometer safely, measure V and I and heating time, record ΔT and calculate c=VIt/(mΔT); repeat and evaluate heat loss. PAG12 research: frame a question (e.g. GPS timing or radioactive tracers), compare reliable online/offline sources and evidence, note date/author, synthesize an answer and cite sources accurately.
- Across practical work, CPAC requires (1) follow written procedures; (2) independently choose/use instruments and methodically control variables, adjust issues and select accurate measurement strategies; (3) identify hazards and apply safety measures; (4) make accurate observations and sufficient precise data with units; (5) use software/tools, research and cite sources. The learner's performance and contemporaneous record must show individual competence across all five. /04 remains a separate teacher-assessed endorsement; written method answers cannot award it.
What to do in an assessment
- For any method specify independent/dependent/control variables; apparatus range/resolution; safe setup; interpolation, zero and alignment; a raw-data table with units; repeats; graph/calculation; uncertainty; and a conclusion justified by data.
- Use a caliper/micrometer with zero correction for small lengths; interpolate analogue scales; select multimeter range before connecting; on the oscilloscope multiply vertical divisions by volts/division and horizontal divisions by time-base. Apply the relevant PAG-specific procedure above, including set-square/plumb-line and data-logger options for PAG1.
- For Young modulus calculate A=πd²/4 and E=(L/A)gradient; for waves use two-source maxima or the resonance/grating/double-slit geometry; for LED Planck plot photon energy in joules against frequency; for gas/capacitor/SHM/heating methods process the stated controlled data and evaluate uncertainty and systematic loss.
In plain language
Method marks come from showing how a safe, repeatable measurement leads to an answer; only actual practical evidence can earn the separate endorsement.
Self-check
A capacitor's ln V against time gradient is −2.0 s⁻¹. Find τ and say whether this calculation passes /04.
Show the answer
τ=−1/gradient=0.50 s. No: /04 depends on practical-record and CPAC evidence, not this written calculation.
Earlier topic checklist
These earlier topic ticks are separate from the reviewed points above and do not count towards that progress.
Physics topic list
This is a topic overview, not a complete specification checklist. Check the official course for all assessed content, options and your exam year.
The exact course specification for this overview has not been confirmed. Check the qualification code and any A/B pathway with your school before using this list.
Tick each item off as you revise. Ticks are saved on this device only.
These ticks keep your earlier topic checklist. They do not count towards the new reviewed requirements above. Its numbering may be internal; use the linked references above for the exact reviewed source requirements.
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