Explain why a room heated by a radiator warms up throughout, even in parts of the room far from the radiator, by describing the process of convection.

Cambridge International IGCSE Physics (0625) — 2.3 Transfer of thermal energy · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A central-heating radiator is fixed to the wall of a room. After the radiator is switched on, the air throughout the entire room gradually warms up.

Model answer (4 marks)

The air touching the radiator is heated and expands, becoming less dense. It rises, creating a low‑pressure zone near the radiator. Cooler, denser air from elsewhere in the room then moves in to replace the rising warm air. This continuous cycle of rising warm air and sinking cool air establishes a convection current that carries thermal energy throughout the room.

Examiner tips

  • Use the word "convection" and describe the rise of warm air and fall of cool air
  • Show the sequence: heating → expansion → lower density → rise → replacement by cool air → circulation
  • Mention that the process repeats, forming a current

Common mistakes

  • Confusing conduction with convection
  • Failing to explain why the warm air rises (density change)
  • Omitting the replacement of warm air by cooler air

Mark scheme (4 marks)

  1. The air in contact with the radiator is heated and expands
  2. The heated air becomes less dense and rises
  3. Cooler, denser air sinks and moves towards the radiator to replace the rising warm air
  4. This sets up a convection current that circulates thermal energy throughout the room

Key terms in this question

convection

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