A microphone converts sound waves into electrical current variations. Explain how a microphone works, and describe how a loudspeaker then uses those current variations to reproduce sound.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A singer performs into a microphone connected by a wire to a loudspeaker. The loudspeaker reproduces the sound on the other side of a large stage.
Model answer (5 marks)
Pressure variations in the sound waves act on the microphone’s diaphragm, causing it to move.
The moving diaphragm carries a coil that passes through the magnetic field of a fixed magnet, so a current (or potential difference) is induced in the coil – the generator effect.
The induced current varies in proportion to the pressure variations of the original sound wave.
In the loudspeaker the varying current flows through a coil situated in the field of a fixed magnet, producing a force on the coil that makes it move.
The moving coil drives the speaker cone or diaphragm, which vibrates and creates pressure variations in the air that are heard as sound.
The moving diaphragm carries a coil that passes through the magnetic field of a fixed magnet, so a current (or potential difference) is induced in the coil – the generator effect.
The induced current varies in proportion to the pressure variations of the original sound wave.
In the loudspeaker the varying current flows through a coil situated in the field of a fixed magnet, producing a force on the coil that makes it move.
The moving coil drives the speaker cone or diaphragm, which vibrates and creates pressure variations in the air that are heard as sound.
Examiner tips
- Use the word "induced" for the coil in the microphone and "force" for the coil in the loudspeaker.
- Show the chain: sound → diaphragm → coil → current → coil in loudspeaker → cone → sound.
- Mention the magnetic field in both devices.
Mark scheme (5 marks)
- Pressure variations in the sound waves cause the coil (in the microphone) to move
- The moving coil passes through the magnetic field of the fixed magnet, inducing a current / potential difference in the coil (generator effect)
- The induced current varies in proportion to (mirrors) the pressure variations of the original sound wave
- In the loudspeaker, the varying current flows through a coil situated in the field of a fixed magnet, causing a force on the coil making it move
- The moving coil causes the cone / diaphragm to vibrate, producing pressure variations in the air which are heard as sound
Key terms in this question
Related
- All Edexcel A-Level Physics (9PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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