WJEC A-Level Physics Unit 3 Oscillations and Nuclei: a complete overview of circular motion, SHM, thermal physics, ideal gases and nuclear physics

What Unit 3 actually demands

Unit 3 Oscillations and Nuclei opens the A2 year. It begins with the mechanics of rotation and oscillation, circular motion and simple harmonic motion, then moves into the behaviour of matter in bulk through thermal physics and the ideal gas, and finishes with the nucleus through radioactive decay and nuclear energy. The unit is calculation-heavy and rewards confident use of exponentials and the defining SHM equation.

This guide walks through the six topics of the unit in specification order, then sets out the exam patterns WJEC repeats. Each topic has a matching dot-point page with practice questions; this overview ties them together.

Circular motion

An object moving in a circle at constant speed is accelerating, because its velocity direction changes. WJEC uses angular velocity $\omega = \frac{2\pi}{T}$, links it to speed by $v = r\omega$, and gives the centripetal acceleration $a = \frac{v^2}{r} = r\omega^2$ and centripetal force $F = \frac{mv^2}{r}$, directed towards the centre.

Vibrations and SHM

Simple harmonic motion is defined by $a = -\omega^2 x$. WJEC covers the sinusoidal solutions, the energy exchange between kinetic and potential, the period of a mass-spring system and a simple pendulum, and damping and resonance, where a system driven at its natural frequency oscillates with large amplitude.

Thermal physics

This topic distinguishes internal energy (the sum of random kinetic and potential energies of particles) from temperature. It uses specific heat capacity $E = mc\Delta\theta$ and specific latent heat $E = mL$ for changes of state, and treats heat transfer and thermal equilibrium.

Ideal gases

The gas laws combine into the ideal gas equation $pV = nRT$. Kinetic theory derives $pV = \frac{1}{3}Nm\overline{c^2}$ and links the mean kinetic energy of a molecule to temperature, $\frac{1}{2}m\overline{c^2} = \frac{3}{2}kT$, giving microscopic meaning to temperature.

Radioactive decay

Radioactive decay is random and spontaneous, following the decay law $N = N_0 e^{-\lambda t}$. WJEC uses activity $A = \lambda N$, the link between half-life and the decay constant, $t_{1/2} = \frac{\ln 2}{\lambda}$, and the properties of alpha, beta and gamma radiation.

Nuclear energy

Mass-energy equivalence $E = mc^2$ explains the mass defect and binding energy. The binding energy per nucleon peaks near iron-56, so fission of heavy nuclei and fusion of light nuclei both release energy by increasing binding energy per nucleon.

How Unit 3 is examined

WJEC Unit 3 is an A2 written paper of about 1 hour 45 minutes carrying 80 marks. Questions follow the specification statements, around 40 per cent of marks are mathematical, and the specified practical on SHM recurs. Drill exponentials for decay and the SHM defining equation until both are automatic, and rehearse mass-energy calculations.

The six topics, dot point by dot point

Each topic has a dot-point answer page with worked exam questions and cross-links. Browse them from this unit overview and the subject hub.

For the official specification

WJEC publishes the full specification, past papers and mark schemes at wjec.co.uk. Always revise from the current specification and WJEC's own past papers, because question style is board-specific.