Explain what is meant by the specific charge of a particle and explain how the specific charge of a proton compares to the specific charge of a nucleus that contains more than one proton.

AQA A-Level Physics (7408) — 3.2.1 Particles · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Specific charge is the charge of a particle divided by its mass.
The specific charge of a proton is greater than that of a nucleus containing more than one proton.
Adding more protons increases the charge of the nucleus, but adding neutrons (and protons) increases the mass.
The mass increases proportionally more than the charge, so the specific charge of the larger nucleus decreases.

Examiner tips

  • Use the definition first, then compare proton vs multi‑proton nucleus.
  • Show the reasoning that mass grows faster than charge.
  • Keep the answer concise – 5 marks only.
  • Use UK spelling (e.g. ‘charge’).

Common mistakes

  • Confusing charge with specific charge.
  • Failing to mention that neutrons add mass but no charge.
  • Giving a long explanation that exceeds the 5‑mark limit.

Mark scheme (5 marks)

  1. Specific charge is the charge of a particle divided by its mass
  2. The specific charge of a proton is greater than the specific charge of a nucleus with more than one proton
  3. Adding more protons increases the charge of the nucleus
  4. Adding neutrons (and protons) increases the mass of the nucleus
  5. The mass increases proportionally more than the charge, so specific charge decreases

Key terms in this question

specific charge · nucleus · proton

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