A singer uses a loudspeaker on stage to hear their own voice played back. Explain how the loudspeaker produces sound from the electrical signal it receives.

Eduqas GCSE Physics — 8.4 Microphones, speakers, oscillating currents in detection · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

The alternating electrical current flows through the voice coil. The current in the coil creates a magnetic field that interacts with the field of the permanent magnet, producing a force on the coil. As the current alternates, the direction of the force reverses, causing the coil and attached cone to vibrate back and forth. The moving cone compresses and rarefies the surrounding air, generating sound waves that the singer hears.

Examiner tips

  • Use the word ‘alternating’ to show you understand the current varies in time.
  • Show the chain: current → force via magnetic field → cone motion → air pressure waves.
  • Mention the coil is in a magnetic field from a permanent magnet.
  • Keep the answer concise – 4 marks, so one sentence per point is enough.

Common mistakes

  • Confusing the coil with the permanent magnet as the source of the magnetic field.
  • Failing to state that the force direction changes with the current. Not linking the cone motion to the creation of sound waves.

Mark scheme (4 marks)

  1. The alternating/oscillating electrical current passes through the coil
  2. The coil experiences a force due to the interaction between the magnetic field (from the permanent magnet) and the current-carrying coil
  3. As the current alternates, the direction of the force on the coil reverses, causing the coil (and cone) to move back and forth / vibrate
  4. The vibrating cone causes compressions and rarefactions in the surrounding air, producing sound waves

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