Loudspeakers & Headphones (Edexcel GCSE Physics)

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Loudspeakers & Headphones

Higher Tier Only

Microphone

  • A moving coil microphone also work using the principles of electromagnetic induction
  • The convert the pressure variations in sound waves into variations in current in electrical circuits

moving-coil-microphone, IGCSE & GCSE Physics revision notes

A moving coil microphone

  • When sound waves reach the microphone, the pressure variations cause the diaphragm to vibrate
    • This in turn causes the coil to move back and forth, through the magnetic field

  • As it does so, the coil cuts through the field lines, inducing an alternating potential difference in the coil and therefore an alternating current

Loudspeakers & Headphones

  • Loudspeakers and headphones convert electrical signals into sound
    • They work due to the motor effect

  • They work in the opposite way to microphones
  • A loudspeaker consists of a coil of wire which is wrapped around one pole of a permanent magnet

loudspeaker-cross-section, IGCSE & GCSE Physics revision notes

Diagram showing a cross-section of a loudspeaker

  • An alternating current passes through the coil of the loudspeaker
    • This creates a changing magnetic field around the coil

  • As the current is constantly changing direction, the direction of the magnetic field will be constantly changing
  • The magnetic field produced around the coil interacts with the field from the permanent magnet
  • The interacting magnetic fields will exert a force on the coil
    • The direction of the force at any instant can be determined using Fleming’s left-hand rule

  • As the magnetic field is constantly changing direction, the force exerted on the coil will constantly change direction
    • This makes the coil oscillate

  • The oscillating coil causes the speaker cone to oscillate
    • This makes the air oscillate, creating sound waves

Examiner Tip

Microphones and loudspeakers look very similar, but they do very different things. When tackling a question on either of them, make sure you are writing about the right one!

The explanation of the loudspeaker is very similar to the explanation of a motor, however direct current is used in a d.c motor and alternating current is used in a loudspeaker or headphone. You need to learn how both work.

When explaining how a loudspeaker works remember to refer to the alternating current and the changing magnetic field that it creates.

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.