1.5.12Motion, Forces and Energy
Nuclear Fission and Nuclear Fusion — Cambridge IGCSE Co-ordinated Sciences 0654 - Physics Revision Notes & Topical Questions
5 min read 7 parts Lesson 35 of 36
Part 1 of 5Nuclear fission
What happens
- What happens A large, unstable nucleus, such as uranium, splits into two smaller nuclei.
- The splitting releases a large amount of energy.
Where it is used
- Where it is used Fission is the energy source in nuclear power stations, where the fuel is held in a reactor.
- The energy is released in a controlled way and used to heat water and generate electricity.
Part 2 of 5Nuclear fusion
What happens
- What happens Two small nuclei, such as hydrogen nuclei, join together to form a larger nucleus.
- A huge amount of energy is released.
Where it occurs
- Where it occurs Fusion is the process that releases energy in the Sun and other stars.
- It needs extremely high temperature and pressure, which are found in the core of a star.
Part 3 of 5Comparing the two processes
| Feature | Fission | Fusion |
|---|---|---|
| Change to nuclei | Large nucleus splits into smaller ones | Small nuclei join into a larger one |
| Starting nuclei | Large nuclei, such as uranium | Small nuclei, such as hydrogen |
| Energy released | Large amount | Huge amount |
| Conditions | Occurs in a nuclear reactor | Extremely high temperature and pressure |
| Example | Nuclear power station | The Sun |
Part 4 of 5Energy from the nucleus
1Nuclear change
- Nuclear change Nuclei are rearranged by splitting or joining.
2Energy released
- Energy released The products have less stored nuclear energy than the starting nuclei, so energy is transferred out.
3Useful transfer
- Useful transfer In a power station the energy heats water to steam, which drives turbines and generators.
Part 5 of 5Fission and fusion in the real world
Fission fuel
- Fission fuel Nuclear power stations use large nuclei such as uranium.
- The energy released by splitting them heats water to make steam, and the steam turns turbines connected to generators.
Fusion in stars
- Fusion in stars In the Sun, hydrogen nuclei fuse together to make larger nuclei.
- The huge energy output of this process is why the Sun shines and keeps the Earth warm.
Why fusion is hard on Earth
- Why fusion is hard on Earth Nuclei repel one another because they are all positively charged.
- Only at extremely high temperature and pressure do they move fast enough and get close enough to fuse,
- which makes fusion difficult to achieve in a power station.
What you must be able to do
- What you must be able to do You are not asked for the detailed mechanism,
- but you must be able to state clearly how fission and fusion differ in what happens to the nuclei.
Key terms
| Term | Meaning |
|---|---|
| Nuclear fission | The splitting of a large nucleus into smaller nuclei, releasing energy. |
| Nuclear fusion | The joining of small nuclei to form a larger nucleus, releasing energy. |
| Nuclear reactor | A device in which fission is controlled to release energy steadily. |
| Nucleus | The dense central part of an atom that contains protons and neutrons. |
Avoid these mistakes
1
Swapping the two processes. Fission splits, and fusion fuses.
2
Saying the Sun uses fission. It releases energy by fusion.
3
Forgetting the conditions for fusionextremely high temperature and pressure, as in a star's core.
4
Describing the energy released as chemical energy. It comes from changes in the nuclei, and not from changes in bonds between atoms.
5
Saying fission joins atoms of uranium together. It splits a uranium nucleus into smaller nuclei.
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