# A scientist is investigating the potential of nuclear fusion as a future energy source. Explain why nuclear fusion releases energy, and why it is difficult to achieve on Earth.

> OCR A-Level Physics A (H556) — 6.3 Nuclear and particle physics · Explain · 5 marks

> Nuclear fusion is the joining of two small, light nuclei to form a larger, heavier nucleus. Scientists have been trying for decades to harness fusion as a clean energy source, but it has proved extremely challenging to sustain the reaction under controlled conditions.

## Mark scheme (5 marks)

1. In fusion, two small/light nuclei join to form a larger/heavier nucleus
2. The mass of the heavier nucleus produced is less than the total mass of the two original nuclei
3. The 'missing' mass is converted into energy, released as radiation
4. High temperatures and pressures are needed to overcome the electrostatic repulsion between the positively charged nuclei
5. These extreme conditions (very high temperatures/pressures) cannot easily be maintained/achieved on Earth

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics A (H556)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-scientist-is-investigating-the-potential-a23373e1) · Published by Druglandscape Ltd.