Back to Daily Question archive

A2 Daily A Level Physics question

2026-06-27 OCR A Nuclear II: mass–energy; binding energy per nucleon; fission/fusion (qual.) OCR-A Module 6.4.2: Mass–energy and binding energy; binding energy per nucleon (qualitative) OCR-A Module 6.4.3: Induced fission and fusion (qualitative energetics)

A revision poster lists average binding energy per nucleon (BE/A): U-235 = 7.6 MeV, typical fission fragments near A ≈ 120 = 8.5 MeV, deuterium (2H) = 1.1 MeV, helium-4 (4He) = 7.1 MeV. A student compares two energy-generation processes: (1) Fission: one U-235 nucleus splits into two fragments near A ≈ 120. (2) Fusion: two deuterium nuclei ultimately form one helium-4 nucleus. Assume the energy released per nucleon is approximately the increase in BE/A from initial to final nuclei. Based on these figures, which statement must be true?

  1. A Fission ≈ 6.0 MeV per nucleon; fusion ≈ 0.9 MeV per nucleon, so fission releases more.
  2. B Fission ≈ 0.9 MeV per nucleon; fusion ≈ 0.9 MeV per nucleon, so they are similar.
  3. C Fission ≈ 0.9 MeV per nucleon; fusion ≈ 6.0 MeV per nucleon, so fusion releases more. (correct)
  4. D Fission ≈ 0 MeV per nucleon; fusion ≈ 0 MeV per nucleon, since higher binding energy means energy is absorbed.

Answer

The correct answer is C.

Correct: C — Fission ≈ 0.9 MeV per nucleon; fusion ≈ 6.0 MeV per nucleon, so fusion releases more. A uses the right numbers but swaps them, a common misconception that heavy-nucleus fission must release more per nucleon. B ignores that the change for fusion is much larger: 7.1 − 1.1 = 6.0 MeV/n versus 8.5 − 7.6 = 0.9 MeV/n. C is correct because the increases are 0.9 MeV/n (fission) and 6.0 MeV/n (fusion), so fusion is about 6–7 times larger per nucleon. D misunderstands binding energy: a higher BE per nucleon means products are more tightly bound and energy is released, not zero or absorbed.

Try today's guest Daily MCQ A Level Physics MCQ practice Problem-solving previews