GCSE Physics (AQA)

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Loudspeakers

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Magnetism and electromagnetism The motor effect

Loudspeakers

3:49 Applying the Motor Effect
Spec 4.7.2.4
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  • Loudspeakers and headphones convert alternating current into sound waves using the motor effect.
  • Both devices operate on the same principles, with headphones being a smaller scale version.
  • Alternating current is supplied to the speaker, which constantly changes direction.
  • The speaker converts electrical energy into sound waves, which travel as vibrations of air molecules.
  • Speakers are a key application of magnets, often explained in exams.
  • Loudspeakers use a special magnet with two circular poles, creating a magnetic field from the outside to the center or vice versa.
  • A coil is wrapped around the inner pole of the magnet and connected to a circuit to carry the alternating current.
  • A cone, or diaphragm, is attached to the coil and moves with it, usually made of paper or thin material.
  • The alternating current causes the motor effect, resulting in a force on the coil that alternates directions rapidly.
  • The motor effect occurs when a wire carrying a current perpendicular to the magnetic field experiences a force.
  • The coil experiences a force along the pole, changing direction as the current changes direction.
  • This causes the coil and attached cone to oscillate back and forth, creating oscillations similar to vibrations.
  • The oscillations of the cone cause pressure variations in the surrounding air, producing sound waves.
  • The cone is shaped to push air molecules rhythmically, creating sound waves.
  • The frequency of the sound waves matches the frequency of the alternating current.
  • A stronger current results in more air disturbance, creating louder sounds.

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