Explain what happens to electromagnetic radiation when it is absorbed by a surface, and why some surfaces are better at absorbing radiation than others.

Eduqas GCSE Physics — 6.2 Interactions of electromagnetic radiation with matter · Explain · 4 marks · View as Markdown

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

Dark, matt surfaces and light, shiny surfaces behave differently when electromagnetic radiation falls on them.

Model answer (4 marks)

When electromagnetic radiation is absorbed, its energy is transferred to the atoms and molecules of the surface. The absorbed energy raises the kinetic energy of the particles, so the temperature of the surface increases.

Dark, matt surfaces absorb more radiation because their colour and texture allow the photons to be taken up by many electrons and vibrational modes. Light or shiny surfaces have high reflectivity; most photons are reflected rather than absorbed, so less energy is transferred and the surface stays cooler.

Examiner tips

  • Use the phrase ‘energy is transferred to the surface’ and link it to ‘temperature rises’.
  • Mention that dark matt surfaces absorb more and shiny surfaces reflect more to show contrast.

Common mistakes

  • Confusing absorption with scattering or reflection.
  • Failing to explain why dark surfaces absorb more (colour/texture).
  • Omitting the temperature rise step.

Mark scheme (4 marks)

  1. When electromagnetic radiation is absorbed, its energy is transferred to the surface/material
  2. This causes the temperature of the surface/material to increase (the surface warms up / heats up)
  3. Dark, matt surfaces absorb more radiation (than light/shiny surfaces)
  4. Light, shiny surfaces reflect more radiation, so less is absorbed

Key terms in this question

absorbed · electromagnetic radiation

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