Explain how a microphone converts sound waves into an electrical current.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A singer performs into a microphone on stage. The microphone is connected to an amplifier so the sound can be heard throughout the venue.
Model answer (4 marks)
Pressure variations in sound waves cause the diaphragm to vibrate, pulling the coil inside the microphone with it.
The coil moves relative to the magnetic field produced by a permanent magnet.
This relative motion induces a potential difference across the ends of the coil (generator effect).
The induced current varies in proportion to the pressure variations, so the electrical signal matches the sound signal.
The coil moves relative to the magnetic field produced by a permanent magnet.
This relative motion induces a potential difference across the ends of the coil (generator effect).
The induced current varies in proportion to the pressure variations, so the electrical signal matches the sound signal.
Examiner tips
- Use the word ‘induced’ to show understanding of EM induction.
- Show the chain: sound → diaphragm → coil movement → relative motion → induced EMF → current.
- Keep the answer concise – 4 marks, one point per sentence.
- Mention the coil is inside a magnetic field to satisfy the ‘relative motion’ point.
Common mistakes
- Confusing the diaphragm with the coil – the coil is the part that moves in the field.
- Failing to mention the magnetic field or relative motion – essential for EM induction.
- Using vague terms like ‘creates a signal’ without linking to pressure variations.
Mark scheme (4 marks)
- Pressure variations in sound waves cause the coil (inside the microphone) to move
- The coil moves relative to (through) the magnetic field / relative motion exists between the coil and the magnet
- A potential difference is induced across the ends of the coil (generator effect)
- The induced current varies in proportion to the pressure variations of the sound waves, so the electrical signal matches the sound signal
Key terms in this question
Related
- All Edexcel GCSE Physics (1PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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