Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
6.43P Describe nuclear fusion as the creation of larger nuclei resulting…
Full specification wording
Topic 6 – Radioactivity: 6.43P Describe nuclear fusion as the creation of larger nuclei resulting in a loss of mass from smaller nuclei, accompanied by a release of energy, and recognise fusion as the energy source for stars
Nuclear fusion joins light nuclei, such as the hydrogen isotopes deuterium and tritium, into a heavier nucleus, for example helium.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 39 of 42
Study notes
From the checked teaching notes for this specification point.
The idea
Nuclear fusion joins light nuclei, such as the hydrogen isotopes deuterium and tritium, into a heavier nucleus, for example helium. The product nucleus has slightly less mass than the total mass of the nuclei that combined, and this mass difference appears as released energy, because mass and energy are linked. Fusion therefore needs very high temperature and pressure so that nuclei overcome their electrostatic repulsion and come close enough to combine. In stars, including the Sun, gravity supplies the pressure and the core temperature is high enough for hydrogen nuclei to fuse into helium, so fusion is the energy source that keeps stars shining. Distinguish fusion from fission: fusion builds larger nuclei from smaller ones, whereas fission splits a large nucleus into smaller ones.
What earns the marks
- Identifies fusion as the joining of smaller nuclei to create a larger nucleus.
- States that the total mass of the products is slightly less than the mass of the original nuclei.
- Links the loss of mass to the release of energy.
- Recognises that fusion is the energy source for stars such as the Sun.
- Distinguishes fusion from fission by noting that fusion combines light nuclei rather than splitting a heavy one.
Common mistakes and how to put them right
Confuses fusion with fission.
Put it right: Keep fusion as the joining of light nuclei and fission as the splitting of a heavy nucleus.
Claims that mass simply disappears with no energy released.
Put it right: State that the lost mass appears as released energy.
Says fusion happens easily at room temperature.
Put it right: Note that very high temperature and pressure are needed to overcome repulsion between nuclei.
Names the Sun's energy as coming from chemical burning.
Put it right: Identify fusion of hydrogen nuclei as the star's energy source.
Exam tips
- Read the question stem carefully to check whether it asks about fusion, fission or both before choosing an option.
- Look for the option that mentions both a larger nucleus being formed and energy being released.
- Eliminate options that describe splitting a heavy nucleus, because those describe fission, not fusion.
- When a question mentions stars, connect the answer to hydrogen nuclei fusing to form helium.
Try the lesson
The start of the Topic 6 – Radioactivity: 6.43P Describe nuclear fusion as the creation of larger nuclei resulting in a loss of mass from smaller nuclei, accompanied by a release of energy, and recognise fusion as the energy source for stars lesson, made from checked teaching notes for this specification point.
Have a go first
In a star, small nuclei join together to make a larger nucleus. What is this process called?
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