A student sets up a simple generator by spinning a rectangular coil of wire between the poles of two permanent magnets. The coil is connected to a sensitive ammeter. Explain how a current is produced in the coil, and describe two changes the student could make to increase the size of the current generated.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student sets up a simple generator by spinning a rectangular coil of wire between the poles of two permanent magnets. The coil is connected to a sensitive ammeter.
Model answer (5 marks)
A relative motion between the coil and the magnetic field induces a potential difference across the ends of the coil, which drives a current through the ammeter because the coil is part of a closed circuit.
To increase the current:
1. Spin the coil faster – a higher angular speed gives a larger induced EMF.
2. Either use more turns of wire in the coil or place the coil in a stronger magnetic field – both increase the induced EMF and thus the current.
To increase the current:
1. Spin the coil faster – a higher angular speed gives a larger induced EMF.
2. Either use more turns of wire in the coil or place the coil in a stronger magnetic field – both increase the induced EMF and thus the current.
Examiner tips
- State the cause of the induced EMF – relative motion and magnetic field. Mention that the coil is part of a closed circuit. Give two specific, valid changes: speed and either turns or field strength.
Common mistakes
- Failing to mention that the coil is part of a complete circuit. Suggesting changes that do not affect EMF, e.g. changing wire colour or resistance without justification.
Mark scheme (5 marks)
- There is relative motion between the coil (conductor) and the magnetic field
- A potential difference is induced across the ends of the coil / conductor
- Because the coil is part of a complete circuit, a current flows
- First valid change: increase the speed of rotation of the coil
- Second valid change: increase the number of turns / coils of wire OR increase the strength of the magnetic field
Related
- All Edexcel A-Level Physics (9PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Simple harmonic motion and damping questions
- Explain why alternating current (AC) must be used in the primary coil of a trans…
- A loudspeaker is connected to the output of an audio amplifier. Explain how the …
- Electricity generated at a power station is transmitted across the country throu…
- A microphone converts sound waves into electrical current variations. Explain ho…