How does a microphone work?

A moving-coil microphone turns sound into an electrical signal by electromagnetic induction.

GCSE Physics

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

In more detail

Sound waves make a diaphragm vibrate, and a coil attached to the diaphragm moves within the field of a permanent magnet. As the coil moves it cuts magnetic field lines, inducing a varying potential difference (and current) that copies the pattern of the sound wave. It is the exact reverse of a loudspeaker.

Key points for the exam

  • It uses electromagnetic induction (movement → voltage).
  • The induced current varies in step with the sound wave.
Exam tip: Loudspeaker = motor effect (current → movement); microphone = induction (movement → current).

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