# A swimming pool appears shallower than it actually is when viewed from above the water surface. Explain why the pool appears shallower than its true depth.

> WJEC A-Level Physics (Wales) — 2.6 Refraction of light · Explain · 5 marks

> When a lifeguard looks straight down into a swimming pool, the bottom of the pool appears to be much closer to the surface than it really is.

## Mark scheme (5 marks)

1. Light travels from the bottom of the pool through water into air (at the water surface)
2. Light changes direction / is refracted at the boundary between water and air
3. As light moves from water (denser) into air (less dense), it bends away from the normal
4. The observer's eye traces the refracted ray back in a straight line, so the apparent source of light appears higher / closer to the surface than the actual source
5. This makes the bottom of the pool appear closer to the surface / the pool appear shallower than it truly is

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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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