# Explain how a colour filter works and describe what happens when white light passes through a red filter and then through a blue filter placed immediately after it.

> WJEC A-Level Physics (Wales) — 6.2 Particle physics and the standard model (A-Level only) · Explain · 5 marks

> White light is made up of all the colours of the visible spectrum. Colour filters are used in theatres, photography and scientific equipment to select specific colours of light.

## Mark scheme (5 marks)

1. A colour filter only allows light of a single colour (single frequency) to pass through
2. A red filter absorbs all colours except red / only transmits red light
3. Only red light reaches the blue filter
4. The blue filter absorbs red light (because it only transmits blue light)
5. No light emerges / the combination appears black / complete darkness results

## Key terms

- [colour filter](https://www.gradenine.co.uk/glossary/colour-filter)
- [white light](https://www.gradenine.co.uk/glossary/white-light)
- [colour](https://www.gradenine.co.uk/glossary/colour)

## 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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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-a-colour-filter-works-fbb0afc4) · Published by Druglandscape Ltd.