Cambridge O Level Physics · Syllabus 5054 · Nuclear Physics
Nuclear Fusion
What is Nuclear Fusion?
Nuclear fusion is the formation of a larger nucleus by combining two smaller nuclei, with the release of energy. It is the energy source for stars.
This definition is part of the Nuclear Physics chapter in Cambridge O Level Physics.
Questions students ask about Nuclear Fusion
What is the difference between nuclear fission and nuclear fusion?
Fusion is the joining of two small nuclei to form a larger nucleus, releasing energy; it is the energy source for stars. Fission is different: a heavy nucleus such as uranium-235 absorbs a neutron, becomes unstable and splits into two daughter nuclei, releasing energy and two or more neutrons. Those released neutrons can go on to cause further fissions, producing a chain reaction — something fusion does not do.
Last reviewed Syllabus 2026-2028