When a student shines a beam of visible light onto a sheet of glass, some of the light is reflected, some is absorbed, and some is transmitted through the glass. Explain what happens to the energy of the photons that are absorbed by the glass.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Different materials interact with electromagnetic radiation in different ways. When radiation strikes a material, it can be reflected, absorbed, or transmitted.
Model answer (4 marks)
The absorbed photons transfer their energy to the atoms or electrons in the glass.
The atoms/electrons are raised to a higher energy level (they become excited).
They then return to a lower energy level and re‑emit a photon.
The frequency (or wavelength) of the re‑emitted photon depends on the energy difference between the levels, so it may be different from the incident photon.
The atoms/electrons are raised to a higher energy level (they become excited).
They then return to a lower energy level and re‑emit a photon.
The frequency (or wavelength) of the re‑emitted photon depends on the energy difference between the levels, so it may be different from the incident photon.
Examiner tips
- Use the exact terms ‘excited’, ‘energy level’, ‘re‑emit a photon’.
- Show the energy transfer chain: photon → atom/electron → excitation → emission.
- Mention that the emitted photon can have a different frequency to the absorbed one.
Common mistakes
- Saying the energy is simply lost as heat without mentioning excitation and re‑emission.
- Using vague phrases like ‘the light is absorbed’ instead of ‘photons transfer energy to atoms/electrons’.
Mark scheme (4 marks)
- The absorbed photons transfer their energy to the atoms/electrons in the glass
- The atoms/electrons are raised to a higher energy level (excited)
- The atoms/electrons return to a lower energy level and re-emit a photon
- The frequency/wavelength of the re-emitted photon depends on the energy difference between the levels / the emitted photon may have a different frequency to the incident photon
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
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- Decode the mark scheme abbreviations →
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