GCSE Physics Revision — Nuclear Fission & Fusion
Revise Nuclear Fission & Fusion for GCSE Physics with a topic explanation, worked example and common mistakes. Check the board notes for specification differences.
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What is Nuclear Fission & Fusion?
Nuclear fission is the splitting of a large, unstable atomic nucleus (like uranium) into two smaller nuclei, releasing a large amount of energy and several neutrons. Nuclear fusion is the process of joining two light nuclei together to form a heavier nucleus, also releasing a vast amount of energy. Fission is used in nuclear power stations, while fusion is the process that powers the Sun.
Board notes: Fission is covered by all boards (AQA, Edexcel, OCR). Fusion is also covered, but often in less detail. The concept of a chain reaction in fission is a key point.
Step-by-step explanationWorked examples
Worked example
In a nuclear fission reactor, a Uranium-235 nucleus absorbs a neutron and splits into two smaller nuclei, releasing 200 MeV of energy and 3 more neutrons. What is this process called and why is it a chain reaction? Solution: This is nuclear fission. It is a chain reaction because the neutrons released can go on to cause further U-235 nuclei to split, releasing even more neutrons and energy in an escalating cascade.
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Common mistakes
- 1Confusing fission and fusion. Fission is splitting, fusion is joining. A simple mnemonic is 'fission has an 'i' for splitting'.
- 2Thinking that both processes are easily controlled. While fission is used in power stations, controlling fusion for power generation is extremely difficult and is still in the experimental stage.
- 3Underestimating the energy released. Both fission and fusion release significantly more energy per kilogram of fuel than chemical reactions like burning fossil fuels.
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Frequently asked questions
What is the difference between nuclear fission and fusion?
Fission is the splitting of a heavy nucleus into lighter ones. Fusion is the joining of two light nuclei to form a heavier one. Both release large amounts of energy.
Why is it so difficult to generate electricity from nuclear fusion?
Fusion requires extremely high temperatures and pressures to overcome the electrostatic repulsion between the positively charged nuclei and force them to fuse. Creating and containing these conditions on Earth is a major scientific and engineering challenge.