Nuclear Fusion
Understand Nuclear Fusion for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) physics topic: nuclear fusion joins two light nuclei into a heavier one, releasing energy, and is the process that powers stars.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Nuclear fusion is the joining of two light nuclei to form a heavier nucleus. This is a Triple-only topic, and it is the process that powers stars.
In fusion, some of the mass of the two nuclei is converted into energy, which is released as radiation. This is why fusion releases far more energy per kilogram than fission.
Fusion is extremely difficult to achieve on Earth. Both nuclei are positively charged, so they repel each other strongly. Enormous temperatures and pressures are needed to overcome that repulsion and bring them close enough to fuse. Those conditions exist naturally in stars but are very hard to create and contain in a reactor.
Revision notes
The fusion process
Two light nuclei join to form a heavier nucleus.
Some of the mass of the original nuclei is converted into energy, which is released as radiation. Fusion releases far more energy per kilogram than fission.
Why it is difficult
Both nuclei are positively charged, so they repel each other strongly.
Enormous temperatures and pressures are required to give the nuclei enough energy to overcome this repulsion and get close enough to fuse.
Fusion versus fission
Fusion joins light nuclei; fission splits a heavy one.
Fusion requires extreme conditions but produces no long-lived radioactive waste. Fission is achievable now but produces radioactive waste requiring long-term storage.
Key points
- Fusion joins two light nuclei into a heavier one.
- Some mass is converted into energy.
- The energy is released as radiation.
- Fusion powers stars.
- Nuclei repel because both are positive.
- Enormous temperatures and pressures are needed.
Worked examples
Example 1
Describe what happens during nuclear fusion. [2 marks]
Model answer
Two light nuclei join together to form a heavier nucleus (1 mark). Some of the mass of the original nuclei is converted into energy, which is released as radiation (1 mark).
Example 2
Explain why very high temperatures and pressures are needed for fusion. [3 marks]
Model answer
Both nuclei are positively charged (1 mark), so they repel each other strongly (1 mark). Extremely high temperatures and pressures are needed to give them enough energy to overcome this repulsion and get close enough to fuse (1 mark).
Example 3
State one difference between nuclear fusion and nuclear fission. [2 marks]
Model answer
Fusion joins two light nuclei together to form a heavier one (1 mark), whereas fission splits a large unstable nucleus into two smaller ones (1 mark).
Common mistakes
Confusing fusion and fission.
Fusion joins; fission splits. The names are easily swapped under pressure.
Saying fusion requires a neutron to start.
That is fission. Fusion requires extreme temperature and pressure.
Not explaining the repulsion.
Both nuclei are positive, which is why they repel and why the conditions must be extreme.
Saying no energy is released.
Mass is converted into energy and released as radiation.
Exam tips
- Keep fusion and fission clearly distinct.
- Explain the difficulty through positive charge and repulsion.
- Say mass is converted into energy.
- Remember this is a Triple-only topic.
Key terms
- Nuclear fusion
- The joining of two light nuclei to form a heavier one.
- Repulsion
- The pushing apart of two positively charged nuclei.
- Radiation
- The form in which fusion energy is released.
- Star
- A body powered by nuclear fusion.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.