# A student states: 'The Doppler effect explains why light from distant galaxies is red-shifted. The faster a galaxy moves away from Earth, the greater the increase in the wavelength of its light.' Explain what is meant by red-shift and describe what the pattern of red-shift observations from distant galaxies tells us about the universe.

> Pearson Edexcel International GCSE Physics (4PH1) — 8.3 Cosmology · Explain · 4 marks

## Mark scheme (4 marks)

1. Red-shift is the observed increase in the wavelength of light emitted by a galaxy moving away from Earth / the wavelength of light from a distant galaxy is longer than expected
2. The more distant the galaxy, the greater (larger) its red-shift / the faster it is moving away from Earth
3. All distant galaxies are moving away from us / the universe is expanding
4. This is consistent with / provides evidence for the Big Bang theory, in which the universe originated from a single point and has been expanding ever since

## Key terms

- [red-shift](https://www.gradenine.co.uk/glossary/red-shift)
- [Doppler effect](https://www.gradenine.co.uk/glossary/doppler-effect)
- [wavelength](https://www.gradenine.co.uk/glossary/wavelength)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](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/a-student-states-the-doppler-effect-587085a9) · Published by Druglandscape Ltd.