Edexcel International A Level Physics Thermodynamics Exam Questions

About Edexcel International A Level Physics Thermodynamics

Thermodynamics is part of Unit 5: Thermodynamics, Radiation, Oscillations and Cosmology in Edexcel International A Level Physics. It covers heating and changes of state using specific heat capacity and specific latent heat, the meaning of internal energy and absolute zero, and the behaviour of ideal gases. You use pV = NkT, the gas laws and the kinetic theory result ½m<c^2> = (3/2)kT to link temperature to molecular motion. Heating experiments are also common contexts for practical skills. Examiners often ask for multi-stage heating calculations, kinetic theory explanations of gas pressure and the meaning of absolute zero.

What you need to know

• Specific heat capacity ΔE = mcΔθ, where c is the energy needed to raise 1 kg by 1 K.
• Specific latent heat ΔE = LΔm. During a change of state, energy increases molecular potential energy and temperature remains constant.
• Internal energy Internal energy is the sum of the random kinetic and potential energies of the molecules. Absolute zero is the temperature at which internal energy is a minimum.
• Ideal gases pV = NkT, with T in kelvin. At constant temperature pV is constant (Boyle's law); at constant volume p is proportional to T.
• Kinetic theory Gas pressure results from molecules changing momentum when colliding with the walls. Mean kinetic energy per molecule ½m<c^2> = (3/2)kT.

Common mistakes in Thermodynamics

• Using °C in pV = NkT. Convert to kelvin.
• Saying temperature increases while a substance is melting.
• Forgetting one stage in a multi-stage heating problem, such as heating the water after melting.
• Using pV = nRT with N, or mixing moles and molecules.
• Defining absolute zero as where all motion stops. Use minimum internal energy.

Try three Thermodynamics exam-style questions