O Level / IGCSE Physics chapter 2: Thermal physics MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
90 exam-style questions on Thermal physics, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A gas is kept at constant temperature while its volume is halved. What happens to its pressure, and why?
A
it halves, because the particles slow down
B
it doubles, because the particles hit the walls more often
C
it stays the same, because temperature is constant
D
it doubles, because the particles move faster
Show answer
Answer: B. At constant temperature the particles keep the same speed, but in half the volume they strike the walls twice as often, so pressure doubles (pV = constant).
2. A fixed mass of gas at constant temperature has a pressure of 2.0 × 105 Pa when its volume is 30 cm3. Which other pair of values lies on the same pressure–volume curve?
A
1.0 × 105 Pa and 15 cm3
B
1.5 × 105 Pa and 40 cm3
C
3.0 × 105 Pa and 45 cm3
D
4.0 × 105 Pa and 60 cm3
Show answer
Answer: B. pV must stay at 2.0 × 105 × 30 = 6.0 × 106. Only 1.5 × 105 × 40 = 6.0 × 106. The other pairs treat p and V as directly proportional.
3. Why are metals good conductors of thermal energy?
A
their particles are far apart
B
they contain free electrons that carry energy quickly through the metal
C
they have a low density
D
they do not expand when heated
Show answer
Answer: B. All solids conduct by lattice vibrations, but metals also have free electrons that move through the metal, transferring energy much faster.
4. Rods of copper, glass and wood, all of the same length and thickness, each have a small bead of wax stuck to one end. Their other ends are placed in the same beaker of hot water. Which observation identifies the best thermal conductor?
A
its wax melts first
B
its wax takes the longest time to melt
C
its wax never melts
D
its end in the water becomes the hottest
Show answer
Answer: A. Energy reaches the wax fastest along the best conductor, so its wax melts first. Here that is copper; the wax on the glass and wood (poor conductors) melts much later or not at all.
5. When a liquid boils, energy is supplied but its temperature does not rise. What is this energy used for?
A
increasing the speed of the particles
B
making the particles larger
C
breaking the particles into atoms
D
overcoming the attractive forces between the particles so they can move far apart
Show answer
Answer: D. Latent heat is the energy needed to change state. It does work against the forces between the particles, separating them; the average kinetic energy, and so the temperature, stays the same.
6. A syringe is sealed at the end. When it is full of air, the plunger can be pushed in a long way. When it is full of water, the plunger hardly moves. Why?
A
the water particles are already touching, but the air particles have large spaces between them
B
the water particles are larger than the air particles
C
the air particles are smaller and can be squashed
D
the water particles move faster than the air particles
Show answer
Answer: A. In a gas the particles are far apart, so pushing them closer is easy. In a liquid they are already close together, so the liquid is almost incompressible. The particles themselves do not change size.
7. A solid is heated at a constant rate. Its temperature rises from 20 °C to 80 °C in 2.0 minutes, then stays at 80 °C for 8.0 minutes before rising again. Which conclusion is correct?
A
it melts at 20 °C and boils at 80 °C
B
no energy reaches it during the 8.0 minutes at 80 °C
C
melting takes four times the energy used to warm the solid
D
its particles speed up during the 8.0 minutes at 80 °C
Show answer
Answer: C. Energy is supplied at a constant rate, so energy is proportional to time: 8.0 minutes of melting takes 4 times the energy of the 2.0 minutes of warming. While it melts, the energy separates the particles, so the temperature (average kinetic energy) stays the same.
8. Which statement describes evaporation but not boiling?
A
it happens at one fixed temperature
B
bubbles form throughout the liquid
C
it happens only at the surface and at any temperature
D
it needs a source of heat
Show answer
Answer: C. Evaporation occurs from the surface at any temperature; boiling occurs throughout the liquid at the boiling point.
9. On a cold morning, a metal bench and a wooden bench in a park are both at 5 °C. The metal bench feels much colder to touch. Why?
A
metal conducts thermal energy away from the hand faster
B
the metal is at a lower temperature than the wooden bench
C
metal lets the cold flow into the hand more quickly than wood
D
wood radiates thermal energy into the hand, but metal does not
Show answer
Answer: A. Both benches are at the same temperature. Metal is a good conductor, so it carries thermal energy away from your warmer hand quickly and your skin cools. "Cold" does not flow: energy flows from hot to cold.
10. What is the temperature called at which the particles of a gas have the least possible kinetic energy?
A
0 °C
B
100 °C
C
absolute zero, −273 °C
D
room temperature
Show answer
Answer: C. Absolute zero (0 K, −273 °C) is the lowest possible temperature, where particle motion is at its minimum.
90, each with the answer and a short explanation, across 3 topics: Kinetic particle model of matter, Thermal properties and temperature, Transfer of thermal energy. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Physics chapter 2 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
