O Level Physics: Thermal physics — Practice Questions (Cambridge 5054)

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — Cambridge International holds copyright in its own papers. Use these alongside the official past papers available from your board.

Most questions practise a skill tested in the June 2025 Paper 22. After each answer there is a tip and, where a paper question matches the skill, the real question to try next.

---

Questions

1. (a) State what is meant by the specific heat capacity of a material. (b) An aluminium block of mass 0.60 kg is heated by a 50 W electric heater for 4.0 minutes. The specific heat capacity of aluminium is 900 J/(kg °C). Assuming all the energy from the heater goes into the block, calculate the rise in temperature of the block. [4]

2. An engineer is choosing a liquid to pump around a hot machine to carry thermal energy away from it. Should the engineer choose a liquid with a high or a low specific heat capacity? Explain your choice. [2]

3. A single gas particle of mass 4.8 × 10⁻²⁶ kg travels at 500 m/s towards the wall of a container. It hits the wall at right angles and rebounds at the same speed. (a) State what is meant by momentum. (b) Calculate the size of the change in momentum of the particle. (c) Explain why the particle exerts a force on the wall. [4]

4. A sealed metal can of air is left in strong sunshine and becomes hot. The volume of the can does not change. Use the particle model to explain the rise in pressure of the trapped air. [3]

5. A bicycle pump is sealed at the end so that no air can escape. It contains 60 cm³ of air at a pressure of 100 kPa. The piston is pushed in slowly until the volume is 24 cm³. The temperature of the air stays the same. (a) Calculate the new pressure of the air. (b) Explain, in terms of particles, why the pressure is greater at the smaller volume. [4]

6. A swimmer steps out of a pool on a warm, windy day and feels cold even though the air is warm. Using ideas about particles, explain why evaporation of the water cools the swimmer, and why the wind makes the effect stronger. [3]

7. A saucepan has a copper base and a plastic handle. Explain why copper is used for the base and plastic for the handle, and describe how thermal energy is transferred through the copper base. [3]

---

Answers

1. (a) The energy needed to raise the temperature of 1 kg of the material by 1 °C [1]. (b) Energy supplied E = P × t = 50 × 240 = 12 000 J [1]; Δθ = E ÷ (m × c) = 12 000 ÷ (0.60 × 900) [1] = 22 °C (22.2 °C) [1].

Tip: convert minutes to seconds before using E = P × t, and rearrange c = ΔE ÷ (mΔθ) before you substitute.

Try the real question next: Cambridge O Level Physics 5054, June 2025, Paper 22, Question 8.

2. A large specific heat capacity [1]. Each kilogram of liquid can then absorb a lot of thermal energy for only a small rise in its own temperature, so it carries more energy away from the machine without getting too hot [1].

Tip: say what “large specific heat capacity” means in practice: more energy absorbed per kilogram for each degree of temperature rise.

Try the real question next: Cambridge O Level Physics 5054, June 2025, Paper 22, Question 8.

3. (a) Momentum = mass × velocity [1]. (b) The velocity reverses, so the change in velocity is 500 − (−500) = 1000 m/s [1]; change in momentum = 4.8 × 10⁻²⁶ × 1000 = 4.8 × 10⁻²³ kg m/s [1]. (c) The wall changes the particle’s momentum, so the wall exerts a force on the particle (force = rate of change of momentum); by Newton’s third law the particle exerts an equal and opposite force on the wall [1].

Tip: when something bounces back at the same speed, its change in momentum is twice its original momentum, not zero, because velocity has a direction.

Try the real question next: Cambridge O Level Physics 5054, June 2025, Paper 22, Question 3.

4. At a higher temperature the particles have more kinetic energy and move faster [1]. They hit the walls more often [1] and with more force (a bigger change in momentum per collision), so the force per unit area, which is the pressure, increases [1].

Tip: give both effects of faster particles: more frequent collisions and harder collisions. “The particles expand” is wrong, because the particles themselves do not get bigger.

Try the real question next: Cambridge O Level Physics 5054, June 2025, Paper 22, Question 3.

5. (a) pV = constant, so p₂ = p₁V₁ ÷ V₂ = 100 × 60 ÷ 24 [1] = 250 kPa [1]. (b) The same number of particles is in a smaller space, so they hit the walls more frequently [1]; the average force on each unit area of wall is larger, so the pressure is greater [1].

Tip: pV = constant only works when the mass of gas and its temperature stay the same, and both volumes must be in the same unit.

6. The most energetic (fastest) water molecules escape from the surface [1], so the average kinetic energy of the molecules left behind decreases, and the water, and the skin it touches, becomes colder [1]. The wind carries away the escaped vapour molecules, so fewer return to the liquid and evaporation happens faster [1].

Tip: the key word is “average”: evaporation removes the fastest molecules, so the average speed of those left falls, which means a lower temperature.

7. Copper is a good thermal conductor, so energy passes quickly from the flame to the food [1]; plastic is a poor conductor (insulator), so the handle stays cool enough to hold [1]. In the copper, energy is transferred by conduction: vibrating atoms pass energy to neighbouring atoms, and free (delocalised) electrons carry energy quickly through the metal [1].

Tip: name the process (conduction) and the mechanism; for metals, mention free electrons as well as atomic vibrations.

---

Where marks are usually lost

• Leaving time in minutes when calculating energy from power.
• Saying particles “expand” or “get bigger” when a gas is heated.
• Mentioning only more frequent collisions, and not harder collisions, when temperature rises.
• Forgetting that velocity reverses on a rebound, so the change in momentum is 2mv.
• Explaining evaporative cooling without saying it is the faster molecules that escape.