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Practice questions · Thermal radiation

No particles required.

Six original Cambridge-style questions on what thermal radiation is, how temperature affects it, which surfaces emit and absorb best, and how it differs from conduction and convection.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Hold on to these facts

Infrared, no medium, black is best.

01
[3 marks]

State what thermal radiation is, what type of wave it consists of, and whether it can travel through a vacuum.

  • It is the transfer of energy by waves (without needing a material). ✓
  • The waves are infrared (electromagnetic) waves. ✓
  • It can travel through a vacuum (no medium is needed). ✓
02
[2 marks]

State which kind of surface is the best emitter of thermal radiation, and which kind is the best absorber.

  • Best emitter: a dull (matt) black surface. ✓
  • Best absorber: also a dull black surface (a good absorber is a good emitter). ✓
03
Analysis
[2 marks]

A flask designed to keep drinks hot has shiny silvered inner walls. Explain how this helps to keep the drink hot.

  • A shiny silvered surface is a poor emitter of radiation. ✓
  • So the hot drink loses energy by radiation only very slowly, staying hot for longer. ✓
04
Analysis
[2 marks]

The panel of a solar water heater is usually painted dull black. Explain why this colour is chosen.

  • A dull black surface is a good absorber of radiation. ✓
  • So it absorbs as much of the Sun's radiation as possible, heating the water more effectively. ✓
05
Analysis
[2 marks]

State the main way in which thermal radiation differs from conduction and convection.

  • Radiation does not need a medium (any material) to travel, so it works through a vacuum. ✓
  • Conduction and convection both need particles of a material, so they cannot occur in a vacuum. ✓
06
Analysis
[3 marks]

Two identical cans are filled with hot water at the same temperature. One has a dull black surface, the other a shiny surface. Predict which cools faster and explain your answer.

  • The dull black can cools faster. ✓
  • A dull black surface is a good emitter, so it radiates energy quickly. ✓
  • The shiny surface is a poor emitter, so it radiates energy slowly and stays hot longer. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.