A bicycle dynamo contains a permanent magnet that spins close to a coil of wire. As a cyclist pedals faster, the dynamo produces a larger voltage. Explain why spinning the magnet faster causes a larger voltage to be induced in the coil.

Eduqas GCSE Physics — 8.3 Induced potential and transformers · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

1. The spinning magnet creates a changing magnetic field through the coil.
2. A changing magnetic field induces a potential difference (voltage) in the coil.
3. When the magnet spins faster, the magnetic field changes more rapidly.
4. A greater rate of change of magnetic field induces a larger potential difference, i.e. a higher voltage.

Examiner tips

  • Use the word ‘induce’ and ‘changing magnetic field’ to match the mark scheme.
  • Show the causal link: faster spin → faster change → higher voltage.
  • Keep each point short and to the point to fit the 4‑mark structure.

Common mistakes

  • Confusing the magnet’s speed with the coil’s speed; only the magnet’s motion matters.
  • Failing to mention that the voltage is proportional to the rate of change of magnetic flux.
  • Using vague phrases like ‘more electricity’ instead of ‘higher voltage’.

Mark scheme (4 marks)

  1. Spinning magnet produces a changing magnetic field (through the coil)
  2. A changing magnetic field induces a potential difference (voltage) in the coil
  3. Spinning faster means the magnetic field changes more rapidly / the rate of change of the magnetic field is greater
  4. A greater rate of change of magnetic field induces a larger potential difference / voltage

Related

More Induced potential and transformers questions

▶ Try answering this question with AI marking (free) →