# Explain what happens to a beam of monochromatic light as it passes from air into a glass block and then back out into air on the other side, including what happens to its speed, wavelength, and direction at each boundary.

> AQA A-Level Physics (7408) — 3.3.2 Refraction, Diffraction and Interference · Explain · 5 marks

## Mark scheme (5 marks)

1. The light slows down as it enters the glass (from air into glass).
2. The wavelength decreases as the light enters the glass.
3. The light bends towards the normal as it enters the glass (because it is entering a denser medium).
4. As the light exits the glass back into air, its speed and wavelength increase back to their original values.
5. The light bends away from the normal as it exits the glass into air (less dense medium), and if the surfaces are parallel the ray emerges travelling in the same direction as the incident ray (though displaced).

## Key terms

- [wavelength](https://www.gradenine.co.uk/glossary/wavelength)
- [monochromatic](https://www.gradenine.co.uk/glossary/monochromatic)

## Related

- [Revision notes for AQA A-Level Physics (7408)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-what-happens-to-a-beam-c48e0763) · Published by Druglandscape Ltd.