A student moves a bar magnet into a coil of wire connected to a sensitive ammeter. The ammeter needle deflects. Explain why a current is induced in the coil and describe two ways the student could increase the size of the induced current.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
A change in the magnetic field through the coil changes the magnetic flux linkage. By Faraday’s law this changing flux induces an e.m.f. (potential difference) in the coil, which drives a current that deflects the ammeter needle.
To increase the induced current the student could:
1. Move the magnet more quickly, increasing the rate of change of flux.
2. Use a stronger magnet or increase the number of turns in the coil, both of which increase the magnitude of the induced e.m.f. and thus the current.
To increase the induced current the student could:
1. Move the magnet more quickly, increasing the rate of change of flux.
2. Use a stronger magnet or increase the number of turns in the coil, both of which increase the magnitude of the induced e.m.f. and thus the current.
Examiner tips
- Use the phrase ‘changing magnetic flux linkage’ to show understanding of Faraday’s law.
- Mention the e.m.f. explicitly as the driving force for the current.
- Give two distinct methods: speed of motion and coil/magnet strength/turns.
- Keep the answer concise and to the point.
Common mistakes
- Confusing the direction of the induced current with the direction of the magnet’s motion.
- Failing to mention the e.m.f. as the cause of the current.
- Using vague terms such as ‘more magnet’ without specifying strength or number of turns.
Mark scheme (4 marks)
- Moving the magnet into the coil changes the magnetic field through the coil (change in magnetic flux linkage)
- This changing magnetic field induces a voltage (potential difference / e.m.f.) in the coil, which drives a current
- First valid method to increase the induced current — e.g. move the magnet faster / increase the speed of movement
- Second valid method to increase the induced current — e.g. use a stronger magnet OR increase the number of turns on the coil
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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