AQA GCSE Physics

Revision Notes

4.4.4 Nuclear Fusion

Nuclear Fusion

  • Small nuclei can react to release energy in a process called nuclear fusion
  • Nuclear fusion is defined as:

When two light nuclei join to form a heavier nucleus

  • This process requires extremely high temperatures to maintain
    • This is why nuclear fusion has proven very hard to reproduce on Earth
  • Stars use nuclear fusion to produce energy
  • In most stars, hydrogen atoms are fused together to form helium and produce lots of energy

nuclear fusion, IGCSE & GCSE Physics revision notes

Two hydrogen nuclei are fusing to form a helium nuclei

  • The energy produced during nuclear fusion comes from a very small amount of the particle’s mass being converted into energy
  • Albert Einstein described the mass-energy equivalence with his famous equation:

E = m × c2

  • Where:
    • E = energy released from fusion in Joules (J)
    • m = mass converted into energy in kilograms (kg)
    • c = the speed of light in metres per second (m/s)
  • The amount of energy released during nuclear fusion is huge:
    • The energy from 1 kg of hydrogen that undergoes fusion is equivalent to the energy from burning about 10 million kilograms of coal

Worked Example

An example of a hydrogen fusion reaction which takes place in stars is shown here.

Fusion equation, downloadable IGCSE & GCSE Physics revision notes

Which of the following is a valid reason as to why hydrogen fusion is not currently possible on Earth?

A   Hydrogen fusion produces dangerous radioactive waste

B   Hydrogen nuclei require very high temperature to fuse together

C   Hydrogen is a rare element that would be difficult to get large amounts of

D   Hydrogen fusion does not produce enough energy to be commercially viable


    • Hydrogen nuclei have positive charges
    • So two hydrogen nuclei would have a repulsive force between them
    • High temperatures are required to give the nuclei enough energy to overcome the repulsive force
    • The answer is not A because the products of the hydrogen fusion shown in the reaction is helium
      • Helium is an inert gas
    • The answer is not C because hydrogen is a very abundant element
      • It is the most common element in the universe
    • The answer is not D because hydrogen fusion would produce a huge amount of energy

Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

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