A diamond gemstone is well known for its ability to bend light by a large amount compared with other transparent materials. Explain why light bends when it enters a diamond from air at an angle to the normal, and describe how the amount of bending in diamond compares with that in glass.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Diamonds are cut with many flat faces to make light change direction dramatically as it passes through the stone. This bending of light at a boundary is called refraction.
Model answer (5 marks)
Light travels at a different speed in different media – it slows down when it enters a diamond from air.
Because the speed changes, the direction of the ray changes – this is refraction.
The ray bends towards the normal when it enters the diamond from air.
Diamond slows light down more than glass does – the speed of light in diamond is lower than in glass.
Therefore, for the same angle of incidence, light bends more (has a greater change in direction / a smaller angle of refraction) in diamond than in glass.
Because the speed changes, the direction of the ray changes – this is refraction.
The ray bends towards the normal when it enters the diamond from air.
Diamond slows light down more than glass does – the speed of light in diamond is lower than in glass.
Therefore, for the same angle of incidence, light bends more (has a greater change in direction / a smaller angle of refraction) in diamond than in glass.
Examiner tips
- Use the phrase "light slows down" to show speed change. Mention "bends towards the normal" to show direction. Compare refractive indices: diamond > glass. Show the logical chain: speed change → direction change → greater bending.
Common mistakes
- Failing to state that light slows down in diamond. Confusing the direction of bending (e.g. saying it bends away from the normal). Not comparing the refractive indices of diamond and glass.
Mark scheme (5 marks)
- Light travels at different speeds in different media / light slows down when it enters diamond from air
- Because light changes speed, it changes direction / this change in speed causes the light to bend
- The ray bends towards the normal when entering the diamond from air
- Diamond slows light down more than glass does / the speed of light in diamond is lower than in glass
- Therefore light bends more (has a greater change in direction / smaller angle of refraction) in diamond than in glass for the same angle of incidence
Key terms in this question
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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