Explain the difference between nuclear fission and nuclear fusion, and state one similarity between the two processes.

WJEC GCSE Physics (Wales) — 2.9 Nuclear decay and nuclear energy · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Nuclear fission is the splitting of a heavy nucleus into two lighter fragments, releasing energy. Nuclear fusion is the joining of two light nuclei to form a heavier nucleus, also releasing energy. Both processes are nuclear reactions that release large amounts of energy.

Examiner tips

Use the terms 'fission' and 'fusion' explicitly; describe the size of nuclei involved. Mention energy release for both. Keep answer concise to fit 4 marks.

Common mistakes

Confusing the direction of the reaction (e.g., saying fusion splits heavy nuclei).
Failing to mention that both are nuclear reactions or that they release energy.

Mark scheme (4 marks)

Nuclear fission is the splitting of a large/heavy nucleus into two smaller nuclei (fragments)
Nuclear fusion is the joining/combining of two small/light nuclei to form a larger nucleus
Both processes release (large amounts of) energy
Both processes involve a change in the nucleus / both are nuclear reactions / both involve a change in nuclear mass

Key terms in this question

nuclear fission · nuclear fusion