Describe what happens to a light wave when it travels from air into glass, in terms of its speed, wavelength, frequency, and direction of travel.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A physicist is investigating how light behaves when it crosses the boundary between air and a glass block. The light ray strikes the glass surface at an angle.
Model answer (4 marks)
The light wave slows down when it enters the glass.
Its wavelength shortens.
Its frequency does not change.
The ray bends towards the normal (it changes direction).
Its wavelength shortens.
Its frequency does not change.
The ray bends towards the normal (it changes direction).
Examiner tips
- Use the word "decreases" for speed and wavelength, "remains unchanged" for frequency, and "bends towards the normal" for direction.
- Include all four points in separate sentences for clarity.
Mark scheme (4 marks)
- The speed of the light wave decreases when it enters the glass
- The wavelength decreases when the light enters the glass
- The frequency remains unchanged / stays the same
- The direction of travel changes / the ray bends towards the normal (as it enters a denser medium)
Key terms in this question
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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