# Explain why a layer of oil floating on water can produce a range of colours when viewed in white light, with reference to what happens at each boundary the light reaches.

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

> When white light shines on a thin layer of oil floating on water, bands of colour are visible across the surface.

## Mark scheme (4 marks)

1. Some light is reflected at the air–oil boundary (top surface of the oil layer)
2. Some light is transmitted into the oil and then reflected at the oil–water boundary (bottom surface of the oil layer)
3. The two reflected beams overlap / combine / interfere
4. Different wavelengths / colours of light are reinforced or cancelled depending on the thickness of the oil, producing different colours

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Physics](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-a-layer-of-oil-e28f8967) · Published by Druglandscape Ltd.