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AQA A-Level Physics Revision

Explore AQA A-Level Physics revision topics. Check the official specification for complete requirements for your exam year and route.

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Course details

AQA · A-Level Physics7408Exam years · 2027

Assessment The assessment includes Paper 1, Paper 2 and Paper 3; see the official specification for the full structure.

Tick a point after revising it. Progress is saved on this device and does not measure mastery.

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.

Options and source

Paper 3 Section B optional topic

  • Astrophysics
  • Medical physics
  • Engineering physics
  • Turning points in physics
  • Electronics

§3.3 Assessment: Paper 3 Section B assesses one selected option from §§3.9–3.13.

Topic group

3.1 Measurements and their errors

1 revision points
  • Core

    Scope: Core · §3.1.1 Use of SI units and their prefixes; §3.1.2 limitations of measurement

    Open revision guidance

    What to know

    • Physical equations use coherent SI units and appropriate prefixes.
    • Instrument resolution limits measurement precision; repeat readings reveal random scatter but do not remove systematic error.
    • Uncertainties in calculated results depend on the measured quantities and the mathematical operation.

    What to do in an assessment

    • Convert all quantities before substituting, retain units and quote precision supported by measurements.
    • Distinguish random variation from calibration/zero error and propose an improvement that targets the cause.

    In plain language

    A ruler with 1 mm divisions cannot justify a length reported to a tiny fraction of a millimetre. Repeating measurements helps with random variation, not an incorrectly zeroed ruler.

    Self-check

    Do repeated readings remove a systematic calibration offset?

    Show the answer

    No. The same systematic offset affects each reading; calibrate or correct the instrument.

Topic group

3.2 Particles and radiation

2 revision points
  • Core

    Scope: Core · §3.2.1.1–3.2.1.7 Constituents, quarks, interactions and conservation

    Open revision guidance

    What to know

    • Protons and neutrons are composite hadrons made from quarks; electrons are leptons.
    • Interactions are mediated by exchange particles; particle processes obey conservation laws such as charge and baryon number where applicable.
    • Antiparticles have equal mass to their corresponding particles and opposite charge.

    What to do in an assessment

    • Use particle symbols and conservation to decide whether a proposed reaction is possible.
    • Check charge and particle numbers independently on both sides.

    In plain language

    Particle reactions must balance conserved quantities. If a proposed reaction creates charge overall, it cannot occur as written.

    Self-check

    What electric charge does an electron’s antiparticle have?

    Show the answer

    A positron has equal positive charge, opposite to the electron.

  • Core

    Scope: Core · §3.2.2.1–3.2.2.4 Photoelectric effect and quantum phenomena

    Open revision guidance

    What to know

    • A photon has energy E = hf; frequency, not intensity, determines energy per photon.
    • Photoelectric emission occurs when photon energy meets or exceeds the material’s work function.
    • Increasing intensity raises the number of photons per second, while increasing frequency raises energy per photon.

    What to do in an assessment

    • Use E = hf and compare with work function; do not confuse intensity with photon energy.
    • Explain why below-threshold light cannot eject electrons even if intensity increases.

    In plain language

    A surface needs a minimum photon energy to release an electron. Making low-frequency light brighter sends more low-energy photons, but none individually reaches the threshold.

    Self-check

    Can raising intensity make photoelectrons emerge if each photon has less energy than the work function?

    Show the answer

    No. Each photon still falls below the emission threshold; frequency must increase.

Topic group

3.3 Waves

1 revision points
  • Core

    Scope: Core · §3.3.1 Progressive and stationary waves; §3.3.2 interference/diffraction/refraction

    Open revision guidance

    What to know

    • Progressive waves transfer energy; stationary waves have nodes and antinodes and do not transfer energy along the pattern.
    • Coherent sources with path difference nλ produce constructive interference; half-integral wavelength difference produces destructive interference.
    • Diffraction is greatest when gap size is comparable to wavelength.

    What to do in an assessment

    • Mark nodes/antinodes and compare path difference with wavelength.
    • For Young’s slits or a grating, relate fringe spacing to wavelength, slit separation and screen distance as specified.

    In plain language

    When two in-step waves meet, their displacements reinforce; when a crest meets a trough, they cancel. Narrow gaps spread waves more strongly.

    Self-check

    What path difference gives constructive interference?

    Show the answer

    An integer multiple of wavelength, nλ.

Topic group

3.4 Mechanics and materials

2 revision points
  • Core

    Scope: Core · §3.4.1 Force, energy and momentum

    Open revision guidance

    What to know

    • Vectors include direction; resolve perpendicular components before combining them.
    • For constant acceleration, equations link displacement, velocity, acceleration and time; Newton’s laws relate force and motion.
    • Momentum p = mv is conserved in an isolated system; work and power describe energy transfer.

    What to do in an assessment

    • Choose signs/directions, draw a free-body diagram and apply equations only when assumptions are met.
    • In a collision, compare total signed momentum before and after.

    In plain language

    A projectile’s horizontal and vertical motions can be analysed separately: gravity changes vertical velocity while horizontal velocity is constant when air resistance is ignored.

    Self-check

    Why does a projectile’s horizontal velocity remain constant in the ideal model?

    Show the answer

    There is no horizontal resultant force when air resistance is neglected.

  • Core

    Scope: Core · §3.4.2.1–3.4.2.2 Bulk properties and Young modulus

    Open revision guidance

    What to know

    • Stress is force per cross-sectional area; strain is extension divided by original length and has no unit.
    • Young modulus E = stress/strain in the linear elastic region.
    • The gradient of a force-extension graph depends on specimen geometry; stress-strain removes those dimensions.

    What to do in an assessment

    • Convert area to m², calculate stress in pascals and use strain as a ratio.
    • Check that the material remains within its proportional/elastic region before using the modulus.

    In plain language

    Stress accounts for how concentrated a force is across a material. Strain compares extension to original length, allowing different-sized samples to be compared.

    Self-check

    A 2 m wire extends by 1 mm. What is its strain?

    Show the answer

    Strain = 0.001/2 = 5.0 × 10⁻⁴.

Topic group

3.5 Electricity

1 revision points
  • Core

    Scope: Core · §3.5.1.1–3.5.1.6 Current electricity

    Open revision guidance

    What to know

    • Current is charge flow per time; potential difference is energy per charge; Ohm’s law applies only where resistance is constant.
    • Resistivity links resistance to length and cross-sectional area; a potential divider shares voltage according to resistance.
    • Electromotive force is energy supplied per charge; terminal p.d. falls under load because of internal resistance.

    What to do in an assessment

    • Use V = ε − Ir to interpret terminal voltage and plot V against I for emf/intercept and internal resistance/gradient.
    • For resistivity, account for wire length, area and instrument uncertainty.

    In plain language

    A battery’s emf is its energy supplied per coulomb. When current flows, some energy is transferred inside its internal resistance, so the terminal voltage is less than the emf.

    Self-check

    What does the y-intercept of a terminal-p.d.-against-current graph represent?

    Show the answer

    The emf, because at zero current there is no internal voltage drop.

Topic group

3.6 Further mechanics and thermal physics

2 revision points
  • Core

    Scope: Core · §3.6.1 Periodic motion

    Open revision guidance

    What to know

    • In simple harmonic motion, acceleration is proportional to displacement from equilibrium and directed toward equilibrium.
    • For SHM, a = −ω²x; period depends on system properties, not amplitude within the relevant ideal model.
    • Energy shifts between kinetic and potential forms during an oscillation.

    What to do in an assessment

    • Use the sign to show restoring acceleration and distinguish displacement from amplitude.
    • At equilibrium speed is maximum; at the turning points speed is zero.

    In plain language

    A spring oscillator is pulled back toward equilibrium. The farther it is displaced, the larger its restoring acceleration in the opposite direction.

    Self-check

    Where is the speed greatest in ideal SHM?

    Show the answer

    At the equilibrium position, where displacement and potential energy are minimum.

  • Core

    Scope: Core · §3.6.2 Thermal physics and ideal gases

    Open revision guidance

    What to know

    • For an ideal gas, molecules move randomly, occupy negligible volume and have negligible intermolecular forces except during collisions.
    • The ideal gas equation pV = nRT links pressure, volume, amount and absolute temperature.
    • Mean molecular kinetic energy is proportional to thermodynamic temperature.

    What to do in an assessment

    • Use kelvin and consistent SI values in pV = nRT.
    • State which quantities are held constant when explaining a pressure-volume-temperature change.

    In plain language

    In the ideal model, gas particles collide elastically and rarely interact between collisions. Heating increases average kinetic energy, raising pressure if volume is fixed.

    Self-check

    Why must temperature be in kelvin in pV = nRT?

    Show the answer

    The gas law uses absolute thermodynamic temperature, whose zero corresponds to zero thermal energy in the model.

Topic group

3.7 Fields and their consequences

3 revision points
  • Core

    Scope: Core · §3.7.2 Gravitational fields

    Open revision guidance

    What to know

    • Gravitational field strength is force per unit mass; gravitational potential is work done per unit mass bringing a small test mass from infinity.
    • A point mass produces an inverse-square field; gravitational potential is negative when zero is defined at infinity.
    • Orbital motion follows from gravitational attraction providing centripetal force.

    What to do in an assessment

    • Keep field strength and potential distinct: N/kg versus J/kg.
    • For satellite calculations, identify orbit radius from the centre of the attracting body.

    In plain language

    Field strength tells how strongly a mass is pulled at a location; potential tells the energy per kilogram associated with that location.

    Self-check

    What is the SI unit of gravitational potential?

    Show the answer

    J/kg (equivalently m²/s²).

  • Core

    Scope: Core · §3.7.3–3.7.4 Electric fields and capacitance

    Open revision guidance

    What to know

    • Electric field strength is force per unit positive charge; potential difference is energy transferred per unit charge.
    • Capacitance C = Q/V; a capacitor stores charge and energy in an electric field.
    • During RC discharge, charge and p.d. decrease exponentially with time constant RC.

    What to do in an assessment

    • Draw field lines from positive to negative and compare spacing.
    • Use logarithmic graph relationships when deriving the time constant from discharge data.

    In plain language

    A capacitor stores separated charge. When connected through a resistor, charge flows back and the p.d. falls; larger resistance or capacitance makes discharge slower.

    Self-check

    What is the time constant of a 2 kΩ resistor and 500 μF capacitor?

    Show the answer

    RC = 2000 × 500×10⁻⁶ = 1 s.

  • Core

    Scope: Core · §3.7.5 Magnetic fields

    Open revision guidance

    What to know

    • A moving charge or current in a magnetic field experiences a force; force direction depends on velocity/current and field direction.
    • Magnetic flux Φ = BA cos θ for a uniform field and flat area; flux linkage is NΦ.
    • Faraday’s law relates induced emf to rate of change of flux linkage.

    What to do in an assessment

    • Define angle convention before calculating flux and distinguish field direction from surface normal.
    • Explain induced emf using changing flux linkage, not simply presence of a magnetic field.

    In plain language

    A stationary coil in a steady field has no induced emf. Changing how much field passes through the coil changes its flux linkage and produces an emf.

    Self-check

    What quantity must change to induce emf in a stationary coil?

    Show the answer

    The magnetic flux linkage through the coil.

Topic group

3.8 Nuclear physics

1 revision points
  • Core

    Scope: Core · §3.8.1 Radioactivity

    Open revision guidance

    What to know

    • Activity is decay rate; it decreases exponentially as unstable nuclei decay.
    • Half-life is independent of the amount of substance in the ideal model.
    • Alpha, beta and gamma have different penetration and ionisation; background must be accounted for in detector readings.

    What to do in an assessment

    • Use decay equations or half-life steps and subtract background where stated.
    • Explain random individual decay alongside predictable large-sample behaviour.

    In plain language

    A sample’s activity falls because fewer undecayed nuclei remain. The decay chance for each nucleus is constant, but the total number decaying each second decreases with the sample.

    Self-check

    What is the relationship between activity and the number of undecayed nuclei?

    Show the answer

    Activity is proportional to the number of undecayed nuclei for a given decay constant.

Topic group

3.9 Astrophysics

1 revision points
  • Core

    Scope: Core · Paper 3 Section B optional topic: Astrophysics · §3.9 Astrophysics: option Astrophysics

    Open revision guidance

    What to know

    • A star’s spectrum contains absorption or emission lines that identify elements and can reveal motion through red-shift.
    • Luminosity, apparent brightness and distance are distinct; standard candles help estimate astronomical distances.
    • The Hertzsprung–Russell diagram relates stellar luminosity and surface temperature.

    What to do in an assessment

    • Use a supplied spectrum or H-R diagram to infer composition, temperature, luminosity or evolutionary stage.
    • Explain red-shift as a measured wavelength change and connect it to recession.

    In plain language

    A star’s spectral lines act like fingerprints. If known lines shift toward longer wavelengths, the star or galaxy is moving away from us.

    Self-check

    What does a red-shifted absorption line indicate?

    Show the answer

    Its observed wavelength is longer than its laboratory wavelength, indicating recession.

Topic group

3.10 Medical physics

1 revision points
  • Core

    Scope: Core · Paper 3 Section B optional topic: Medical physics · §3.10 Medical physics: option Medical physics

    Open revision guidance

    What to know

    • Medical imaging uses mechanisms such as ultrasound reflection, X-ray attenuation and radionuclide detection.
    • Ultrasound depth uses pulse travel time and sound speed; X-ray contrast depends on differing absorption.
    • A method is selected by the required tissue information, resolution, risk and patient context.

    What to do in an assessment

    • State the signal source, interaction with tissue and detector response for the named imaging method.
    • Compare benefits and risks without treating any modality as universally best.

    In plain language

    Ultrasound sends pulses and detects echoes from tissue boundaries; X-rays measure how much radiation passes through different tissues.

    Self-check

    How does ultrasound locate a tissue boundary?

    Show the answer

    It times the reflected pulse; with sound speed, the round-trip travel time gives boundary depth.

Topic group

3.11 Engineering physics

1 revision points
  • Core

    Scope: Core · Paper 3 Section B optional topic: Engineering physics · §3.11 Engineering physics: option Engineering physics

    Open revision guidance

    What to know

    • A force applied at a perpendicular distance creates a moment; angular motion has rotational equivalents to linear motion.
    • An engine’s efficiency compares useful work or energy output with total input.
    • Thermodynamic cycles involve energy transfers and can be assessed using work and heat.

    What to do in an assessment

    • Use the perpendicular lever arm for moment and track units.
    • Compare ideal and real engines through dissipated energy and efficiency.

    In plain language

    A longer lever gives a force more turning effect. An engine cannot convert all supplied energy into useful work because some is transferred to the surroundings.

    Self-check

    How does doubling the perpendicular distance change a moment if force stays fixed?

    Show the answer

    The moment doubles because M = Fd.

Topic group

3.12 Turning points in physics

1 revision points
  • Core

    Scope: Core · Paper 3 Section B optional topic: Turning points in physics · §3.12 Turning points in physics: option Turning points

    Open revision guidance

    What to know

    • The discovery of the electron and photoelectric effect challenged earlier models of matter and light.
    • The photoelectric effect supports quantised photon energy and cannot be explained by classical wave intensity alone.
    • Special relativity changes measurements of space and time at speeds close to the speed of light.

    What to do in an assessment

    • Describe an observation, the prediction of an earlier model and the revised conclusion.
    • Separate evidence from the model used to interpret it.

    In plain language

    Scientific models change when measurements contradict their predictions. The photoelectric effect showed that light energy arrives in packets whose energy depends on frequency.

    Self-check

    Which property determines photon energy in the photoelectric explanation?

    Show the answer

    Frequency: photon energy is E = hf.

Topic group

3.13 Electronics

1 revision points
  • Core

    Scope: Core · Paper 3 Section B optional topic: Electronics · §3.13 Electronics: option Electronics

    Open revision guidance

    What to know

    • Analogue signals vary continuously; digital signals represent values in discrete steps or binary states.
    • Semiconductor components such as diodes and transistors control current.
    • Amplifiers and logic circuits process signals; communication systems may modulate and transmit information.

    What to do in an assessment

    • Read a signal diagram and distinguish amplitude from encoded value.
    • Explain how a named component changes or controls current.

    In plain language

    An analogue microphone voltage can vary smoothly with sound. A digital system samples it and encodes values, making it easier to store and process with logic circuits.

    Self-check

    What is the main distinction between analogue and digital signals?

    Show the answer

    Analogue signals vary continuously; digital signals use discrete values or states.

Topic group

Practical skills: waves

2 revision points
  • Core

    Scope: Core · §7.2 Required practical 1

    Open revision guidance

    What to know

    • Required practical 1 varies frequency, string length, tension and mass per unit length to investigate stationary-wave frequency.
    • A stationary wave has nodes and antinodes; boundary conditions determine allowed wavelengths.
    • Keep tension, length or linear density fixed while changing the chosen independent variable.

    What to do in an assessment

    • Mark node spacing and use adjacent-node separation as half a wavelength.
    • Repeat measurements and explain how uncertainty in node position affects wavelength.

    In plain language

    A stationary pattern forms when waves reflect and interfere. The fixed ends constrain which wavelengths fit the string.

    Self-check

    What is the distance between adjacent nodes in a stationary wave?

    Show the answer

    Half a wavelength.

  • Core

    Scope: Core · §7.2 Required practical 2

    Open revision guidance

    What to know

    • Required practical 2 investigates interference with Young’s slits and a diffraction grating.
    • Fringe spacing depends on wavelength, screen distance and slit separation.
    • Coherent sources are needed for a stable interference pattern.

    What to do in an assessment

    • Measure several fringe spacings, divide by the number of intervals and record screen/slit distances.
    • Use the appropriate grating or slit relation and discuss alignment and fringe-reading uncertainty.

    In plain language

    Two coherent light waves overlap and form bright and dark fringes. Measuring the spacing across several fringes gives a more reliable average.

    Self-check

    Why measure across several fringe gaps?

    Show the answer

    It reduces percentage uncertainty in the average fringe spacing.

Topic group

Practical skills: mechanics

1 revision points
  • Core

    Scope: Core · §7.2 Required practical 3

    Open revision guidance

    What to know

    • Required practical 3 determines g by a free-fall method.
    • For an object released from rest under constant acceleration, s = ½gt².
    • Reaction time, release timing, distance measurement and air resistance can affect the result.

    What to do in an assessment

    • Measure fall distance and time repeatedly; where appropriate use a graph of s against t² to obtain g from its gradient.
    • Identify random and systematic errors and justify a measurement improvement.

    In plain language

    A freely falling object speeds up because of gravity. Relating distance to time squared lets measurements estimate gravitational acceleration.

    Self-check

    If s = ½gt², what is the gradient of s plotted against t²?

    Show the answer

    The gradient is g/2, so g is twice the gradient.

Topic group

Practical skills: materials

1 revision points
  • Core

    Scope: Core · §7.2 Required practical 4

    Open revision guidance

    What to know

    • Required practical 4 determines Young modulus from extension of a material under load.
    • Young modulus is stress divided by strain; the test must remain within the elastic region.
    • Wire length, cross-sectional area, force and extension are all needed.

    What to do in an assessment

    • Measure diameter at several positions with a micrometer and average before calculating area.
    • Measure extension with a suitable method, plot stress against strain and calculate the linear gradient.

    In plain language

    A material’s Young modulus describes how much it strains under stress. Accurate area measurement is important because diameter is squared when finding cross-sectional area.

    Self-check

    Why measure a wire diameter at several positions?

    Show the answer

    To reduce the effect of local irregularity and improve the estimate of cross-sectional area.

Topic group

Practical skills: electricity

2 revision points
  • Core

    Scope: Core · §7.2 Required practical 5

    Open revision guidance

    What to know

    • Required practical 5 finds resistivity using wire length, cross-sectional area, current and potential difference.
    • Resistivity ρ = RA/L and R = V/I.
    • Use a micrometer for wire diameter; heating changes resistance and should be controlled.

    What to do in an assessment

    • Measure several wire lengths and obtain V and I for each; keep current low or allow cooling.
    • Plot resistance against length; the gradient and cross-sectional area determine resistivity.

    In plain language

    Resistance increases with wire length. Measuring that pattern and accounting for the wire’s area reveals the material’s resistivity.

    Self-check

    How do you obtain resistance from voltage and current readings?

    Show the answer

    R = V/I for the paired readings.

  • Core

    Scope: Core · §7.2 Required practical 6

    Open revision guidance

    What to know

    • Required practical 6 measures terminal p.d. as current varies to determine emf and internal resistance.
    • The relation V = ε − Ir gives a straight line of terminal p.d. against current.
    • The y-intercept is emf and the magnitude of the gradient is internal resistance.

    What to do in an assessment

    • Use a variable load, record paired V and I values and avoid short-circuiting the cell.
    • Plot V against I and discuss meter resolution, contact resistance and heating.

    In plain language

    As the load draws more current, more voltage is lost inside the cell’s internal resistance. Extrapolating the graph to zero current estimates emf.

    Self-check

    What does the gradient of terminal voltage against current represent?

    Show the answer

    Negative internal resistance; its magnitude is r.

Topic group

Practical skills: oscillations

1 revision points
  • Core

    Scope: Core · §7.2 Required practical 7

    Open revision guidance

    What to know

    • Required practical 7 investigates simple harmonic motion using a mass-spring system and simple pendulum.
    • Period is time per oscillation; timing many oscillations and dividing reduces reaction-time effects.
    • For a simple pendulum at small angle, period depends on length and g; for a mass-spring oscillator, it depends on mass and spring constant.

    What to do in an assessment

    • Vary one independent variable at a time, time multiple cycles and repeat.
    • Plot a linearised relationship where specified and explain small-angle or low-damping assumptions.

    In plain language

    Timing one swing is difficult because of human reaction time. Timing many swings gives a better average period.

    Self-check

    Why time 20 oscillations rather than one?

    Show the answer

    Dividing the total time by 20 reduces the fractional effect of reaction-time uncertainty.

Topic group

Practical skills: gases

1 revision points
  • Core

    Scope: Core · §7.2 Required practical 8

    Open revision guidance

    What to know

    • Required practical 8 investigates Boyle’s law for a fixed mass of gas at constant temperature.
    • Pressure is inversely proportional to volume when temperature and gas amount are fixed.
    • A p-versus-1/V graph should be linear under ideal conditions.

    What to do in an assessment

    • Change gas volume gradually, allow temperature to return to stable conditions and record pressure.
    • Control temperature and identify leakage or sensor calibration as limitations.

    In plain language

    Compressing the gas increases collision frequency and pressure. Keeping temperature constant isolates the pressure-volume relationship.

    Self-check

    At constant temperature, what happens to pressure when gas volume halves?

    Show the answer

    Pressure doubles.

Topic group

Practical skills: capacitors

1 revision points
  • Core

    Scope: Core · §7.2 Required practical 9

    Open revision guidance

    What to know

    • Required practical 9 investigates charge/discharge and estimates the RC time constant.
    • Capacitor voltage changes exponentially; one time constant during discharge leaves about 37% of its initial value.
    • A log-linear plot can yield the time constant from its gradient.

    What to do in an assessment

    • Use a voltmeter/data logger, record voltage at regular intervals and calculate ln(V/V0) if appropriate.
    • Estimate uncertainty in the time constant and control resistor/capacitor values.

    In plain language

    A capacitor discharges quickly at first and then more slowly. The resistor and capacitor together set the characteristic time scale RC.

    Self-check

    After one time constant of discharge, approximately what fraction of initial charge remains?

    Show the answer

    About 1/e, or 37%.

Topic group

Practical skills: magnetic fields

1 revision points
  • Core

    Scope: Core · §7.2 Required practical 10

    Open revision guidance

    What to know

    • Required practical 10 varies magnetic flux density, current and wire length to investigate motor-effect force.
    • For perpendicular wire and field, F = BIL.
    • The force direction follows current and magnetic field directions.

    What to do in an assessment

    • Vary one factor while keeping others constant and use a balance to detect force change.
    • Reverse current or field and confirm the force reverses; consider wire heating and zero error.

    In plain language

    A wire’s current interacts with the external magnetic field. Increasing current or the length inside the field increases force under otherwise fixed conditions.

    Self-check

    If current doubles while field and wire length stay fixed, what happens to force?

    Show the answer

    Force doubles because F = BIL.

Topic group

Practical skills: electromagnetic induction

1 revision points
  • Core

    Scope: Core · §7.2 Required practical 11

    Open revision guidance

    What to know

    • Required practical 11 uses a search coil and oscilloscope to investigate flux linkage as coil angle changes.
    • Induced emf depends on the rate of change of flux linkage.
    • Coil orientation affects flux through it; rotation produces an alternating signal.

    What to do in an assessment

    • Keep magnet/field strength and rotation rate controlled while changing the angle.
    • Interpret oscilloscope amplitude and explain signal polarity/zero crossings.

    In plain language

    A coil receives the most magnetic flux when its area faces the field and the least when the field runs along its plane. Rotating it changes flux and induces a voltage.

    Self-check

    At what coil orientation is magnetic flux through the coil greatest?

    Show the answer

    When the coil’s area normal is parallel to the magnetic field (the plane of the coil is perpendicular to the field).

Topic group

Practical skills: radioactivity

1 revision points
  • Core

    Scope: Core · §7.2 Required practical 12

    Open revision guidance

    What to know

    • Required practical 12 investigates how gamma count rate varies with distance.
    • For a point source in open geometry, intensity is proportional to 1/r².
    • Background radiation must be measured and subtracted; use shielding and safe handling.

    What to do in an assessment

    • Measure count for the same time at several distances, subtract background and plot corrected count rate against 1/r².
    • Keep source orientation, detector geometry and timing consistent.

    In plain language

    As distance from a small source grows, radiation spreads over a larger area. Doubling distance gives about one quarter of the intensity in the ideal point-source model.

    Self-check

    If distance doubles, what happens to intensity under the inverse-square law?

    Show the answer

    It falls to one quarter.

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