Magnetism & Electromagnetism - 7.2.4 Loudspeakers (Physics Only) (HT Only) (GCSE Physics AQA)

Loudspeakers (Physics Only) (HT Only)

Varying Pressure in Sound Waves

• In electrical circuits the current can be varied. This can be converted into pressure variations in sound waves.
• The current variations are converted into pressure variations through the motor effect. This means that the motor effect is commonly used in loudspeakers and headphones.

Uses of Moving Coils

One practical application of moving coils is in loudspeakers.

Inside a loudspeaker, there is alternating current which passes through coil which is wrapped around a magnet.

There’s a second wire with a separate current passing through it.

The two magnetic fields created interact, causing force to be exerted.

When the current through the coils reverses, the force exerted by the coils will also reverse.

The coils are connected to a cone which vibrates when the coils exert a force. This vibration changes when the current alternates.

We can control the vibration of the cone by changing the frequency of the alternating current. This controls the pitch and volume produced by the loudspeaker.