AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Students should be able to explain how a moving-coil microphone works.
Full specification wording
Microphones (HT only): Students should be able to explain how a moving-coil microphone works.
Build your explanation of a moving-coil microphone around the parts visible in a cross-section diagram.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 2 of 2
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Build your explanation of a moving-coil microphone around the parts visible in a cross-section diagram. The diaphragm is the thin sheet facing the sound, the coil is wound on a former fixed behind it, and the permanent magnet is fixed to the body. Explain the sequence: sound waves cause the diaphragm to vibrate, making the attached coil vibrate with it. As the moving coil cuts the magnetic field lines of the fixed magnet, a potential difference is induced across the coil. This induced potential difference drives a varying current around the circuit. A microphone uses the generator effect, whereas a loudspeaker uses the motor effect to transfer energy in the opposite direction.
What earns the marks
- Identifying that sound waves cause the diaphragm to vibrate.
- Stating that the coil is attached to the diaphragm and vibrates with it.
- Explaining that the moving coil cuts the magnetic field lines of the fixed permanent magnet.
- Stating that this induces a potential difference across the ends of the coil.
- Explaining that the induced potential difference drives a varying alternating current in the closed circuit.
- Comparing with a loudspeaker by stating the microphone uses the generator effect while the loudspeaker uses the motor effect.
Common mistakes and how to put them right
Having the magnet move and the coil stay still, which contradicts standard microphone diagrams.
Describing the current as being produced by the magnet rather than induced in the coil.
Writing a sequence of steps with no cause linking them, such as jumping from sound arriving to current flowing without mentioning the coil cutting field lines.
Claiming that a microphone and a loudspeaker are built from fundamentally different components.
Exam tips
- Annotate the diagram first, then write one sentence for each labelled part to build a logical sequence.
- Ensure your explanation links cause and effect, from the arriving sound wave to the induced current.
Try the lesson
The start of the Microphones (HT only): Students should be able to explain how a moving-coil microphone works. lesson, made from checked teaching notes for this specification point.
Have a go first
In a moving-coil microphone, what is the job of the diaphragm?
Listen
Build your explanation of a moving-coil microphone around the parts visible in a cross-section diagram. The diaphragm is the thin sheet facing the sound, the coil is wound on a former fixed behind it, and the permanent magnet is fixed to the body. Explain the sequence: sound waves cause the diaphragm to vibrate, making the attached coil vibrate with it. As the moving coil cuts the magnetic field lines of the fixed magnet, a potential difference is induced across the coil. This induced potential difference drives a varying current around the circuit. A microphone uses the generator effect, whereas a loudspeaker uses the motor effect to transfer energy in the opposite direction. A strong answer earns marks for these points. identifying that sound waves cause the diaphragm to vibrate. stating that the coil is attached to the diaphragm and vibrates with it. explaining that the moving coil cuts the magnetic field lines of the fixed permanent magnet. stating that this induces a potential difference across the ends of the coil. Exam tip: Annotate the diagram first, then write one sentence for each labelled part to build a logical sequence.
Key words
Say what each word means before you turn the card.
moving-coil microphone
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diaphragm and coil
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fixed magnet
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generator effect
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See every definition
- moving-coil microphone
- A device in which sound waves cause a diaphragm to vibrate, making an attached coil cut the magnetic field lines of a fixed magnet and inducing a potential difference.
- diaphragm and coil
- The thin sheet facing the sound and the coil wound on a former fixed behind it, which vibrates with the diaphragm as sound waves arrive.
- fixed magnet
- The permanent magnet fixed to the body, whose magnetic field lines are cut by the moving coil.
- generator effect
- The effect a microphone uses, whereas a loudspeaker uses the motor effect to transfer energy in the opposite direction.
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