Physics: mechanics, waves, electromagnetism and thermodynamics
The physics section tests mechanics (forces, momentum, energy), wave behaviour, electric and magnetic fields with simple circuits, and thermodynamics including the gas laws and the first law. Expect short calculations plus one explanation question where you must name a law and substitute values.
Core rules
- Mechanics: F=ma; friction f=μN; momentum is conserved in collisions; KE=½mv²; PE=mgh; in projectile motion horizontal velocity is constant while vertical acceleration is −g.
- Waves: v=fλ; refraction follows n₁sinθ₁=n₂sinθ₂; a string fixed at both ends carries standing waves with λ=2L/n.
- Electromagnetism: V=IR; P=VI; force on a current F=BIL sinθ; induced emf ε=−N·dΦ/dt (Faraday); flux Φ=BA cosθ.
- Thermodynamics: PV=nRT; ΔU=Q−W; efficiency = W/Q_in; gas-law temperatures must be in kelvin.
Worked example
A 0.50 kg ball moving at 4.0 m/s strikes a stationary 1.5 kg ball and they stick together. Momentum before = 0.50×4.0 = 2.0 kg·m/s; total mass = 2.0 kg, so v = 1.0 m/s. Kinetic energy before = ½×0.50×16 = 4.0 J; after = ½×2.0×1.0² = 1.0 J; 3.0 J is lost to heat and deformation. Momentum is conserved, kinetic energy is not - that is the point of the question.
Traps that cost marks
Leaving grams or centimetres unconverted; mixing g=9.8 and g=10 within one paper; losing track of sign direction in projectiles; believing a larger flux gives a larger emf when only its rate of change does; using Celsius in PV=nRT; ignoring the direction of friction.
Key skills to drill
Draw a free-body diagram or a before/after momentum table before writing equations.