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Thermal physics

Explain heating, temperature, internal energy and transfer by conduction, convection and radiation.

12 free questions · Notes · Worked solutions

Practise this topic

What you will practise

  • Distinguish temperature from internal energy.
  • Use energy=mass×specific heat capacity×temperature change.
  • Describe conduction, convection and infrared radiation.
  • Explain changes of state using particle ideas and latent heat.

Revision notes

Temperature and internal energy

Temperature indicates how hot a body is and relates to the average kinetic energy of its particles. Internal energy is the total microscopic kinetic and potential energy of the particles.

Specific heat capacity

For a temperature change, energy transferred Q=mcΔT, where c is specific heat capacity in J/(kg °C). Use the temperature difference, not the final temperature alone.

Heat transfer

Conduction transfers energy through particle interactions and free electrons in metals. Convection involves bulk movement of a fluid. Thermal radiation is mainly infrared and can travel through a vacuum.

Changes of state

During a change of state, energy changes particle arrangement or separation while temperature stays constant for a pure substance at fixed pressure. Latent heat Q=mL.

A worked example

A 0.5 kg block is heated from 20°C to 60°C. Its specific heat capacity is 400 J/(kg °C). Find the energy transferred.

  1. Temperature change ΔT=60−20=40°C.
  2. Q=mcΔT=0.5×400×40.
  3. Q=8000 J.

8000 J

Try it yourself

These are original practice questions, not official past-paper questions. Practice points count correct final answers; working is not automatically assessed.

Choose a question to begin.
Question 1 · Standard1 practice point

Which process can transfer thermal energy through a vacuum?

Need a hint?

A vacuum has no particles to conduct or convect heat.

Worked solution
  1. Infrared electromagnetic waves travel through empty space.
Question 2 · Standard1 practice point

What happens to the temperature of pure ice while it melts at its melting point?

Need a hint?

Energy changes the state during melting.

Worked solution
  1. The supplied energy is latent heat for changing state.
  2. Temperature remains constant until melting is complete.
Question 3 · Standard1 practice point

Which equation gives energy needed to heat a mass without a change of state?

Need a hint?

Use the specific heat capacity relationship.

Worked solution
  1. For temperature change, Q=mcΔT.
Question 4 · Standard1 practice point

Why does warm air rise in a room?

Need a hint?

Heating causes air to expand.

Worked solution
  1. The warmed air expands, lowering its density.
  2. Buoyancy makes the less dense air rise.
Question 5 · Foundation2 practice points

How much energy is needed to raise the temperature of 2 kg of water by 5°C? Use c=4200 J/(kg °C).

Need a hint?

Use Q=mcΔT.

Worked solution
  1. Q=2×4200×5.
  2. Q=42 000 J.
Question 6 · Stretch3 practice points

A 0.25 kg metal sample absorbs 3000 J. Its temperature rises by 30°C. Find its specific heat capacity.

Need a hint?

Rearrange Q=mcΔT to find c.

Worked solution
  1. c=Q/(mΔT).
  2. c=3000/(0.25×30)=3000/7.5.
  3. c=400 J/(kg °C).
Question 7 · Standard2 practice points

A 1.5 kg substance has specific heat capacity 800 J/(kg °C). Find the energy needed for a 10°C rise.

Need a hint?

Multiply m, c and ΔT.

Worked solution
  1. Q=1.5×800×10.
  2. Q=12 000 J.
Question 8 · Standard2 practice points

A 2 kg solid melts at constant temperature. Its specific latent heat of fusion is 150 000 J/kg. Find the energy needed to melt it.

Need a hint?

Use Q=mL.

Worked solution
  1. Q=2×150 000.
  2. Q=300 000 J.
Question 9 · Standard2 practice points

A 0.4 kg liquid evaporates. Its specific latent heat of vaporisation is 2 000 000 J/kg. Find the energy required.

Need a hint?

Multiply mass by latent heat.

Worked solution
  1. Q=mL=0.4×2 000 000.
  2. Q=800 000 J.
Question 10 · Stretch3 practice points

A 0.6 kg sample is heated by 18 000 J and warms by 10°C. Find its specific heat capacity.

Need a hint?

Use c=Q/(mΔT).

Worked solution
  1. c=18 000/(0.6×10).
  2. c=18 000/6=3000 J/(kg °C).
Question 11 · Stretch3 practice points

A 100 g sample has specific heat capacity 900 J/(kg °C). It is heated by 20°C. Find the energy transferred.

Need a hint?

Convert 100 g to 0.1 kg first.

Worked solution
  1. m=100 g=0.1 kg.
  2. Q=mcΔT=0.1×900×20.
  3. Q=1800 J.
Question 12 · Standard2 practice points

A 3 kg object at 80°C cools to 50°C. If c=500 J/(kg °C), how much thermal energy leaves it?

Need a hint?

Use the size of the temperature change.

Worked solution
  1. ΔT=80−50=30°C.
  2. Q=3×500×30=45 000 J.

Coverage and sources

Selected IGCSE concepts, with a mix of introductory and more demanding questions. Check your own specification. AI drafted; independent teacher review is pending. Editorial details.

Cambridge IGCSE Physics 0625 syllabus

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