# Explain why objects that behave like a black body are considered ideal emitters and absorbers of radiation, and describe how the temperature of a black body affects the infrared radiation it emits.

> WJEC A-Level Physics (Wales) — 6.3 Stellar evolution and cosmology (A-Level only) · Explain · 5 marks

> Scientists use the idea of a black body to model how stars and other hot objects emit radiation across the electromagnetic spectrum.

## Mark scheme (5 marks)

1. A black body absorbs all radiation that is incident on it (no radiation is reflected or transmitted)
2. A black body is also an ideal emitter of radiation (emits as much radiation as possible at its temperature)
3. At a constant temperature, a black body radiates the same average power that it absorbs
4. The hotter the black body, the greater the infrared radiation it emits in a given time
5. All objects emit and absorb infrared radiation, so a black body is a useful model for any object that absorbs and re-emits radiation (such as a star)

## Key terms

- [black body](https://www.gradenine.co.uk/glossary/black-body)
- [infrared radiation](https://www.gradenine.co.uk/glossary/infrared-radiation)
- [emitter](https://www.gradenine.co.uk/glossary/emitter)
- [absorber](https://www.gradenine.co.uk/glossary/absorber)

## 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-why-objects-that-behave-like-4a917d4c) · Published by Druglandscape Ltd.