A-Level Physics AQA 7408

Thermal energy transfer

Internal energy is the sum of the randomly distributed kinetic energies and potential energies of the particles in a body.

The internal energy of a system is increased when energy is transferred to it by heating or when work is done on it (and vice versa), eg a qualitative treatment of the first law of thermodynamics.

Appreciation that during a change of state the potential energies of the particle ensemble are changing but not the kinetic energies. Calculations involving transfer of energy.

For a change of temperature: $Q = mc∆θ$ where c is specific heat capacity.

Calculations including continuous flow.

For a change of state $Q = ml$ where l is the specific latent heat.

Ideal gases

Gas laws as experimental relationships between p, V, T and the mass of the gas.

Concept of absolute zero of temperature.

Ideal gas equation: $pV = nRT$ for n moles and $pV = NkT$ for N molecules.

$\text{Work done} = p∆V$

Avogadro constant N_A, molar gas constant R, Boltzmann constant k

Molar mass and molecular mass.

Molecular kinetic theory model

Brownian motion as evidence for existence of atoms.

Explanation of relationships between p, V and T in terms of a simple molecular model.

Students should understand that the gas laws are empirical in nature whereas the kinetic theory model arises from theory.

Assumptions leading to $pV = \dfrac{1}{3}Nm(c_{rms})^2$ including derivation of the equation and calculations.

A simple algebraic approach involving conservation of momentum is required.

Appreciation that for an ideal gas internal energy is kinetic energy of the atoms.

Use of average molecular kinetic energy = $\dfrac{1}{2}m(c_{rms})^2 = \dfrac{3}{2}kT = \dfrac{3RT}{2N_A}$

Appreciation of how knowledge and understanding of the behaviour of a gas has changed over time.

Required practical 8:

Investigation of Boyle's law (constant temperature) and Charles’s law (constant pressure) for a gas.