AQA A-Level Physics Paper 2, June 2025: Question 31

1 mark ยท Easy difficulty ยท Multiple Choice

Identify which region of the binding energy per nucleon curve contains nuclei that undergo fission to release energy.

Practise this question

Question

A graph showing average binding energy per nucleon in MeV plotted against nucleon number from 0 to 250. Three shaded regions are highlighted: region P for nucleon numbers from 0 to about 40, region Q near the peak around 60 to 90, and region R for large nucleon numbers between 200 and 250. The multiple choice question asks in which region or regions nuclei undergo fission to release energy, with options A (P only), B (P and R), C (Q and R), and D (R only).

Mark scheme

Show the mark scheme Mark scheme table row for question 31 showing the correct answer is D (R only) with assessment objective AO1.

How to answer it

Binding Energy per Nucleon & Nuclear Reactions

๐Ÿ“Œ What this question tests

Understanding and interpreting the average binding energy per nucleon versus nucleon number (A) graph; identifying the conditions required for energy release in nuclear reactions; and distinguishing between nuclear fusion (light nuclei) and nuclear fission (heavy nuclei).

Question 31

Identifying Regions of Energy Release via Fission

AQA A-Level Physics • Nuclear Physics • 1 Mark • AO1

โœ… Correct Answer: D (R only)

Only nuclei in region R undergo fission to release energy.

  • Fission involves a heavy, less stable parent nucleus splitting into two lighter, more tightly bound daughter nuclei.
  • In region R (nucleon number A > 200), daughter nuclei have a higher average binding energy per nucleon than the original nucleus, resulting in an overall release of energy:
    ฮ”E = (Total BE of products) โˆ’ (Total BE of reactants) > 0

๐Ÿ“ Analysis of Graph Regions

Region Nucleon Range Process for Energy Release
P Low (A < 40) Fusion (nuclei combine to move up the steep gradient towards peak).
Q Peak (A โ‰ˆ 56โ€“60) Most stable nuclei (e.g., โตโถFe). Neither fission nor fusion releases net energy.
R High (A > 200) Fission (large nuclei split into fragments closer to the peak).

๐Ÿ’ก Key Knowledge: Why Energy Is Released

  • Binding Energy per Nucleon: Measures nuclear stability. A higher value means each nucleon is held more tightly within the nucleus.
  • Driving Principle: Any spontaneous or energy-yielding nuclear reaction must result in products with a higher binding energy per nucleon than the starting reactants.
  • Peak at โตโถFe: Iron-56 (near 8.8 MeV per nucleon) represents the maximum stability:
    • Nuclei lighter than iron move right and upwards via fusion.
    • Nuclei heavier than iron move left and upwards via fission.

โŒ Common Errors & Traps

  • Confusing Fission with Fusion: Selecting A (P only) or B (P and R) occurs when students confuse splitting (fission, R) with joining (fusion, P).
  • Choosing Region Q: Region Q is the peak of the curve. Because it is already at maximum binding energy per nucleon, nuclei in region Q cannot release energy through either process.
  • Energy Sign Misconception: Thinking energy release requires a "drop" on this graph. Remember: binding energy is the energy required to completely separate nucleons, so going higher means reaching a lower, more bound energy state.

๐Ÿง  Exam Technique & Rapid Recall

For multiple-choice questions on this classic curve:

  1. Read the process carefully: Highlight whether the question asks for fission (right side / heavy) or fusion (left side / light).
  2. Identify the goal: Both processes move toward the peak at A โ‰ˆ 56 (Iron-56).
    • From the left: Fusion moves P โ†’ Q.
    • From the right: Fission moves R โ†’ Q.
  3. Because the prompt specifies fission, eliminate any option containing P or Q immediately.
Mark Scheme Note: 1 mark awarded for selecting D (AO1 - recall and identify standard nuclear phenomena from graphical data). No partial credit.

Topics

Physics ยท 3.8 Nuclear physics (A-level only)

Question and mark scheme from the AQA A-Level Physics examination, Paper 2, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.