Explain why a black, dull-surfaced metal container of hot water cools down more quickly than an identical shiny, white-surfaced container of hot water at the same initial temperature, when both are placed in the same surroundings.

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).

Model answer (4 marks)

A black, dull‑sided metal container is a good emitter of thermal (infrared) radiation, so it loses energy by radiation more rapidly than a shiny, white‑sided container, which is a poor emitter. Because the black container loses thermal energy faster, its temperature falls more quickly, so it cools down faster than the shiny container.

Examiner tips

  • Use the term ‘emitter of thermal (infrared) radiation’ for the black surface and ‘poor emitter’ for the white surface.
  • Show the causal link: better emission → greater energy loss → faster cooling.
  • Keep the answer concise and use the exact wording from the mark scheme.

Common mistakes

  • Confusing absorption with emission; the question concerns emission of radiation.
  • Using vague phrases like ‘more reflective’ without linking to radiation loss.
  • Failing to mention that the temperature drop is faster, not just that energy loss is greater.

Mark scheme (4 marks)

  1. Black/dull surfaces are good emitters of thermal (infrared) radiation
  2. White/shiny surfaces are poor emitters of thermal (infrared) radiation
  3. The black container therefore loses thermal energy at a greater rate by radiation
  4. Since the black container loses energy faster, its temperature falls more quickly / it cools down faster than the shiny container

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