A generator in a power station produces electricity by electromagnetic induction. Explain how rotating a coil of wire inside a magnetic field produces an induced potential difference, and state what must be true about the coil's motion for the induced potential difference to be at its maximum value.

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 coil is rotated through a magnetic field, so the magnetic flux through the coil changes.
2. The changing flux induces an electromotive force (EMF) in the coil according to Faraday’s law.
3. As the coil turns, the induced EMF alternates in sign, producing a sinusoidal potential difference.
4. The EMF is maximum when the coil is moving perpendicular to the field lines, i.e. when it cuts the field lines at the greatest rate.

Examiner tips

  • Use the phrase ‘changing magnetic flux’ and ‘Faraday’s law’ to show understanding. Show the EMF alternates as the coil rotates. State the condition for maximum EMF: coil moving perpendicular to the field lines. Keep each point concise and use correct terminology.

Common mistakes

  • Confusing ‘parallel to the field lines’ with ‘perpendicular’ for maximum EMF. Forgetting to mention that the EMF alternates in direction as the coil rotates. Using vague terms like ‘moving fast’ instead of ‘perpendicular to the field lines’.

Mark scheme (4 marks)

  1. The rotating coil cuts through magnetic field lines (flux linkage changes)
  2. This induces a potential difference (or EMF) in the coil
  3. The induced potential difference alternates (reverses direction) as the coil rotates
  4. The induced potential difference is at its maximum when the coil is moving parallel to the magnetic field (perpendicular to the field lines) / cutting field lines at the greatest rate

Key terms in this question

induced potential difference · electromagnetic induction

Related

More Induced potential and transformers questions

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