Paper 3 Thermal Physics B Drills

Q1 Kinetic theory derivation logic

An ideal gas contains $N$ molecules of mass $m$ in volume $V$.

1. State three assumptions of the ideal-gas kinetic model. [3]
2. Explain qualitatively how molecular collisions with walls produce pressure. [3]
3. State the result $pV=\frac{1}{3}Nm⟨c^2⟩$ and explain the origin of the factor $1/3$. [2]
4. Use this with $pV=NkT$ to obtain the mean translational kinetic energy. [3]

Q2 Thermodynamic process reasoning

An ideal gas changes from state A to B. It is compressed slowly while thermal contact keeps its temperature constant.

1. State the process type. [1]
2. State $\Delta U$ for the gas. [1]
3. Explain the relationship between heat transfer and work done on the gas. [3]
4. Sketch the shape of the process on a p-V graph. [2]