A generator in a power station uses electromagnetic induction to produce electricity. Explain how changing the speed at which the generator spins affects the induced EMF produced, and describe TWO other changes a technician could make to the generator to increase the induced EMF.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A generator contains a coil of wire that rotates between the poles of a magnet. As the coil spins, an EMF is induced across its ends.
Model answer (5 marks)
Increasing the speed of rotation increases the induced EMF, because the coil cuts through the magnetic field lines more quickly, giving a greater rate of change of magnetic flux.
A technician could:
1. Use a stronger magnet, which increases the magnetic flux density and therefore the induced EMF.
2. Increase the number of turns in the coil, which multiplies the induced EMF.
Alternatively, a technician could wind the coil around an iron core to concentrate the flux, or increase the coil’s area to intercept more field lines.
A technician could:
1. Use a stronger magnet, which increases the magnetic flux density and therefore the induced EMF.
2. Increase the number of turns in the coil, which multiplies the induced EMF.
Alternatively, a technician could wind the coil around an iron core to concentrate the flux, or increase the coil’s area to intercept more field lines.
Examiner tips
- Use the term ‘rate of change of magnetic flux’ to show understanding of Faraday’s law.
- Show the two specific changes (magnet strength and number of turns) and give a third optional method.
- Mention that increasing speed directly increases EMF.
- Use correct UK spelling and concise language.
Common mistakes
- Saying the EMF decreases when speed increases – the opposite is true.
- Failing to mention that the change is due to the rate of change of flux.
- Using vague terms like ‘make it stronger’ without specifying magnet strength or coil turns.
Mark scheme (5 marks)
- Increasing the speed of rotation increases the induced EMF (or decreasing speed decreases it)
- Because the coil cuts through magnetic field lines more quickly / the rate of change of flux is greater
- Increasing the strength of the magnet (using a stronger magnet) increases the induced EMF
- Increasing the number of turns on the coil increases the induced EMF
- Any second valid method correctly stated: e.g. wind the coil around an iron core / use a coil with a larger area
Key terms in this question
electromagnetic induction · induced EMF
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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