OCR A Physics Paper 3 Prep
A focused guide to the big gaps from Papers 1 and 2. Use this to decide what to revise before Unified Physics.
Highest priority revision areas
Start here if you are short on time. These are the areas that feel most likely to be useful for Paper 3 because they were absent, light, or easy to combine with other topics.
Simple harmonic motion
Know the definitions, the graphs and the energy changes. Be ready for displacement, velocity and acceleration graphs, plus damping and resonance.
Capacitors and exponential decay
Practise charging and discharging graphs, time constant, and using natural logs to turn an exponential graph into a straight line.
Electromagnetic induction
Faraday's law, Lenz's law, flux linkage, generators and transformers are all strong candidates for structured calculation questions.
Quantum physics
Revise photons, photoelectric effect, stopping potentials, work function, threshold frequency, electron diffraction and de Broglie wavelength.
Thermal physics
Brownian motion, specific heat capacity, specific latent heat, ideal gases and Maxwell-Boltzmann distributions are all worth a careful look.
Nuclear and medical physics
Half-life, carbon dating, binding energy, fission, fusion, X-ray attenuation, CAT scans and PET scans could easily appear in Paper 3.
Paper 1 gaps to revise
These are mainly from forces, materials, momentum, thermal physics, circular motion and oscillations.
SUVAT and projectiles
- Constant acceleration equations.
- Horizontal and vertical motion treated separately.
- Projectile questions where one direction has constant velocity and the other has acceleration.
- Graph skills: gradient and area under velocity-time graphs.
Drag and terminal velocity
- Why drag increases with speed.
- Falling objects with weight, drag and resultant force.
- Terminal velocity when resultant force is zero.
- Fluid contexts such as a ball bearing falling through oil.
Material properties
- Hooke's law and force-extension graphs.
- Area under force-extension graphs as work done.
- Stress, strain, Young modulus and ultimate tensile strength.
- Ductile, brittle and polymeric materials.
- Elastic and plastic deformation.
Impulse and collisions
- Momentum as a vector quantity.
- Force as rate of change of momentum.
- Impulse as FΔt.
- Area under a force-time graph.
- Conservation of momentum in one and two dimensions.
- Elastic and inelastic collisions.
Brownian motion and kinetic theory
- Brownian motion as evidence for particles moving randomly.
- Smoke particles being hit by air molecules.
- Gas pressure explained by molecular collisions with container walls.
- Links between temperature and molecular kinetic energy.
Specific heat and latent heat
- E = mcΔθ for specific heat capacity.
- E = mL for specific latent heat.
- Electrical practical methods.
- Why temperature stays constant during a change of state.
- Uncertainty, insulation and energy loss evaluation points.
Ideal gases and distributions
- Assumptions of the kinetic model.
- pV = nRT and pV = NkT.
- Maxwell-Boltzmann distribution shape.
- Root mean square speed.
- How temperature changes the distribution.
Circular motion
- Radians, angular velocity and period.
- v = rω.
- a = v²/r = rω².
- F = mv²/r = mrω².
- Banked turns, aircraft in horizontal circles, vertical loops and where the force is greatest.
Simple harmonic motion
- SHM condition: acceleration is proportional to displacement and in the opposite direction.
- a = -ω²x.
- x = A cos(ωt) or x = A sin(ωt).
- vmax = ωA.
- Displacement, velocity and acceleration graphs.
- Energy graphs and exchange between kinetic and potential energy.
Damping and resonance
- Free oscillations compared with forced oscillations.
- Natural frequency.
- Resonance when driving frequency equals natural frequency.
- Amplitude-frequency graphs.
- Effect of damping on the resonance peak.
Paper 2 gaps to revise
These are mainly from electricity, waves, quantum physics, capacitors, electromagnetism, nuclear physics and medical imaging.
Mean drift velocity
- Current as moving charge.
- I = Anev.
- What each symbol means.
- Why drift velocity is usually small even when the circuit responds quickly.
- Conductors, semiconductors and insulators in terms of charge carrier density.
Resistivity and power
- R = ρL/A.
- Resistivity practical for a metal wire.
- Temperature effects in metals and semiconductors.
- Electrical power: P = IV, P = I²R, P = V²/R.
- Energy transfer: W = VIt.
Intensity and interference
- Intensity as power per unit area.
- Intensity is proportional to amplitude squared.
- Inverse square behaviour when radiation spreads out from a point source.
- Superposition, coherence and phase difference.
- Constructive and destructive interference.
Young double slit
- Use λ = ax/D.
- Know what fringe spacing, slit separation and screen distance mean.
- Be ready to explain why the pattern is evidence for the wave nature of light.
- Compare double slit with diffraction grating style questions.
Photons and photoelectric effect
- Photon energy: E = hf and E = hc/λ.
- Electronvolt conversions.
- Work function and threshold frequency.
- Einstein equation: hf = Φ + KEmax.
- Stopping potential and maximum kinetic energy.
- Gold-leaf electroscope and zinc plate explanation.
Electron diffraction and de Broglie
- Electrons showing wave-like behaviour.
- Diffraction through thin polycrystalline graphite.
- de Broglie wavelength: λ = h/p.
- Higher momentum means shorter wavelength.
Capacitor circuits
- Capacitance: C = Q/V.
- Capacitors in series and parallel.
- Charging and discharging through a resistor.
- Time constant: τ = CR.
- Energy stored: W = 1/2 QV, W = 1/2 CV².
Exponential graphs
- Equations like x = x0e-t/CR.
- Linearise by taking natural logs.
- For discharge, plot ln V against t.
- The gradient is negative and linked to 1/CR.
- This skill also links to radioactive decay and X-ray attenuation.
Parallel-plate capacitors
- C = ε0A/d.
- Increasing area increases capacitance.
- Increasing plate separation decreases capacitance.
- Adding a dielectric increases capacitance.
Faraday, Lenz and generators
- Magnetic flux: Φ = BA cosθ.
- Flux linkage: NΦ.
- Induced e.m.f. depends on rate of change of flux linkage.
- Lenz's law gives the direction of the induced e.m.f.
- Simple a.c. generators and transformers.
Particle classification and decay
- Hadrons, leptons and quarks.
- Proton and neutron quark composition.
- Beta minus and beta plus decay.
- Conservation of charge, baryon number and lepton number.
- Do not forget the neutrino or antineutrino.
Nuclear radius and density
- Alpha scattering and the nuclear model.
- Nuclear notation.
- Radius equation: R = r0A1/3.
- Nuclear density calculations using mass divided by volume.
Half-life and carbon dating
- Decay is spontaneous and random.
- Activity: A = λN.
- Half-life and λt1/2 = ln2.
- Decay equations: A = A0e-λt and N = N0e-λt.
- Carbon dating could appear as a longer written explanation with calculations.
Binding energy, fission and fusion
- Mass defect and E = Δmc².
- Binding energy per nucleon.
- Energy released from fission and fusion.
- Balanced nuclear equations.
- Chain reactions and reactor components.
X-rays, CAT and PET
- X-ray tube and production of X-ray photons.
- Attenuation equation: I = I0e-μx.
- Contrast media.
- CAT scanner advantages over a single X-ray image.
- Medical tracers, gamma camera and PET scans.
Cross-topic combinations to practise
Paper 3 likes to mix ideas. The aim is not just to know topics separately, but to spot links between topics.
Generators and simple harmonic motion
This is a very sensible Paper 3 style combination because both topics involve sinusoidal motion or sinusoidal variation.
- Start with rotation. A coil rotates in a magnetic field. The angle between the coil and the field changes continuously.
- Flux changes with angle. Magnetic flux can be written as Φ = BA cosθ. For a rotating coil, the angle changes with time, so the flux changes with time.
- Induced e.m.f. depends on rate of change. Faraday's law says the induced e.m.f. depends on how quickly the flux linkage changes.
- This gives an alternating output. The e.m.f. changes direction every half-turn, so the generator produces an alternating e.m.f.
- The maths looks like SHM. In SHM, displacement often varies as x = A cos(ωt) or x = A sin(ωt). In a generator, flux and e.m.f. also vary sinusoidally.
- Maximum values happen at different points. Flux is maximum when the coil is aligned so the field passes through the largest effective area. The induced e.m.f. is maximum when the flux is changing fastest.
Exponential decay everywhere
Capacitor discharge, radioactive decay and X-ray attenuation all use the same mathematical shape. Practise plotting natural log graphs to get a straight line and using the gradient.
Brownian motion and collisions
Brownian motion links kinetic theory to momentum ideas. The random motion comes from many uneven molecular collisions with tiny visible particles.
Wave-particle evidence
Young double slit supports the wave model of light. Photoelectric effect supports the photon model. Electron diffraction supports the wave nature of particles.
Binding energy and decay
Be ready to combine nuclear equations, mass defect, binding energy per nucleon, fission, fusion and energy release in one messy question.
How to revise this efficiently
Best quick plan: 25 minutes on SHM and generators, 25 minutes on capacitor decay, 25 minutes on quantum, then 25 minutes on nuclear or medical exponential decay.