A theatre costume is made from fabric that only reflects blue light. Explain what colour the costume appears when it is lit by cyan light, and what colour it appears when it is lit by red light.

Eduqas GCSE Physics — 6.4 Colour and frequency · Explain · 4 marks · View as Markdown

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

Cyan light is a mixture of blue light and green light.

Model answer (4 marks)

The fabric only reflects blue light.

• When lit by cyan light, which contains blue light, the fabric reflects the blue component and therefore appears blue.
• When lit by red light, which contains no blue light, the fabric absorbs all of the red light and reflects none, so it appears black.

Examiner tips

  • Use the command word ‘Explain’ – give a short reason for each colour. Mention that the fabric’s reflective property is limited to blue. Show the link between the light’s spectrum and the fabric’s response.

Common mistakes

  • Claiming the costume appears green or cyan – ignoring that the fabric only reflects blue. Saying the costume appears red under red light – forgetting that the fabric does not reflect red. Using vague terms like ‘colourful’ instead of specifying blue or black.

Mark scheme (4 marks)

  1. Cyan light contains blue light (as well as green light)
  2. The fabric reflects the blue component of the cyan light, so the costume appears blue
  3. Red light contains no blue light
  4. The fabric absorbs all the red light and reflects none, so the costume appears black

Key terms in this question

reflects · cyan

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