A wind turbine uses the generator effect to produce electricity. As the blades turn, a coil of wire rotates between two permanent magnets. Explain how the generator effect produces a current in the coil, and state two ways the magnitude of the induced potential difference could be increased.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Wind turbines generate electricity for thousands of homes. Inside the turbine, rotating coils of wire interact with magnetic fields to produce an electrical output.
Model answer (5 marks)
A rotating coil in a magnetic field experiences a changing magnetic flux, which by Faraday’s law induces a potential difference across its ends.
Because the coil is part of a closed circuit, the induced EMF drives a current through the load.
The magnitude of the induced potential difference can be increased by:
1. Increasing the angular speed of the coil (faster rotation).
2. Using stronger permanent magnets or increasing the number of turns in the coil.
Because the coil is part of a closed circuit, the induced EMF drives a current through the load.
The magnitude of the induced potential difference can be increased by:
1. Increasing the angular speed of the coil (faster rotation).
2. Using stronger permanent magnets or increasing the number of turns in the coil.
Examiner tips
- Use the phrase ‘changing magnetic flux’ or ‘wire cuts through field lines’ to show understanding of the generator effect.
- Show the link between induced EMF and current by mentioning a complete circuit.
- Give two specific, valid methods for increasing the EMF – speed, magnet strength, or turns – and explain why each works.
Common mistakes
- Confusing the generator effect with the motor effect (e.g. stating that a current is required to produce the EMF).
- Failing to mention that the coil must be part of a closed circuit for current to flow.
- Giving a method that does not actually increase the induced potential, such as changing the coil’s resistance.
Mark scheme (5 marks)
- The rotating coil experiences a change in magnetic field (or the wire cuts through magnetic field lines)
- This induces a potential difference across the ends of the coil
- Because the coil is part of a complete circuit, a current flows
- First valid method to increase the induced potential difference — e.g. increase the speed of rotation of the coil
- Second valid method to increase the induced potential difference — e.g. use stronger permanent magnets / increase the number of turns on the coil
Key terms in this question
generator effect · potential difference · induced · permanent magnet
Related
- All OCR A-Level Physics B: Advancing Physics (H557) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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