Nuclear fusion — AQA GCSE Physics
Test yourself on Nuclear fusion with AQA GCSE practice questions.
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Nuclear fusion explained
Nuclear fusion is the joining of two light nuclei to form a heavier one.
Read the full explanation
In the Sun and in experimental reactors, hydrogen isotopes fuse to form helium. Getting them to fuse is hard because both nuclei are positively charged and repel strongly, so extremely high temperatures and pressures are needed to bring them close enough; lasers or magnetic confinement are used to reach those conditions. When they do fuse, the heavier nucleus has slightly less mass than the two that formed it, and some of the mass is converted into the energy of radiation. This is the energy source of every main sequence star, where the outward effect of fusion balances the inward gravitational collapse.
Your focus
- Explain how nuclear fusion releases energy, including the conversion of mass into the energy of radiation.
- State the conditions needed for fusion and explain why they are so extreme.
- Compare fusion and fission by the size of the nuclei involved and the direction of the change.
Nuclear fusion exam tips
Marking Points
- one mark for two light or lighter nuclei, such as hydrogen nuclei, fusing together
- one mark for forming a heavier nucleus or a heavier element, for example helium
- one mark for some of the mass of the nuclei being converted into the energy of radiation
- one mark for the very high temperature and pressure needed to overcome the repulsion between positively charged nuclei
Examiner Tips
- 💡Use the phrase 'some of the mass is converted into energy', because that exact idea carries its own mark.
- 💡Name helium as the product if hydrogen is named in the question; it is explicitly allowed.
- 💡Avoid the words 'bonding' and 'colliding' as your main verb; 'fuse' or 'join' is what is credited.
Common Mistakes
- describing fusion as the splitting of a nucleus
- writing that the nuclei bond or collide and stick, which examiners ignore without the mass conversion point
- saying fusion takes place at ordinary temperatures
- confusing nuclear fusion with the melting or fusing of solids
- claiming mass is destroyed rather than converted into the energy of radiation