A student investigates the generator effect by pushing a bar magnet into a coil of wire connected to a sensitive ammeter. Explain what happens to the induced voltage when the student pushes the magnet in more quickly and also uses a coil with a greater number of turns.

Pearson Edexcel International GCSE Physics (4PH1) — 6.2 Electromagnetism · Explain · 4 marks · View as Markdown

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

A bar magnet is pushed into a coil of wire at varying speeds. The coil has different numbers of turns in different trials. The coil is connected to a sensitive ammeter.

Model answer (4 marks)

Pushing the magnet in more quickly increases the rate of change of the magnetic field through the coil, so the induced voltage is larger.

Using a coil with more turns increases the length of wire that experiences the changing magnetic field, so the induced voltage is also larger.

Examiner tips

  • Use the word "rate of change" to link speed with voltage. Mention that more turns = more wire in the field. Show the two effects separately. Keep each point brief and to the point.

Common mistakes

  • Confusing the direction of the induced current with the magnitude of the voltage. Saying the voltage is the same but the current changes. Using vague terms like "more" without explaining the underlying reason.

Mark scheme (4 marks)

  1. Pushing the magnet in more quickly causes the magnetic field through the coil to change more rapidly / increases the rate of change of the magnetic field
  2. A greater rate of change of the magnetic field induces a greater/larger voltage
  3. Increasing the number of turns increases the length of wire / conductor inside the magnetic field
  4. More turns therefore induces a greater/larger voltage

Key terms in this question

generator effect · induced voltage · turns

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