# Explain why a fish swimming underwater is able to see objects above the water surface only within a limited cone of view, even though objects exist all around above the surface.

> Eduqas GCSE Physics — 5.2 Waves at material interfaces · Explain · 4 marks

> Light travels at different speeds in water and in air. When light passes from one medium to another, its direction can change at the boundary.

## Mark scheme (4 marks)

1. Light is refracted / changes direction when it passes from air into water (or water into air) because it changes speed at the boundary
2. Light travelling from water to air at an angle greater than the critical angle undergoes total internal reflection and cannot reach the fish's eye
3. Only light that strikes the water surface at an angle less than the critical angle can pass through into the water and reach the fish
4. This means the fish's entire view of the world above the surface is concentrated / compressed into a narrow cone directly above, limiting what the fish can see

## Related

- [Revision notes for Eduqas GCSE Physics](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-a-fish-swimming-underwater-2681b3a5) · Published by Druglandscape Ltd.