Electromagnets in Everyday Devices

Relays, buzzers, speakers and motors.

A relay uses a small current in a coil to pull an iron armature and flip a switch in a separate circuit, so a weak signal can control a heavy load. A buzzer uses the same idea but the armature breaks its own circuit, so it vibrates rapidly.

A loudspeaker sets a coil in a permanent magnet's field. The audio current makes the coil push and pull, moving a cone that pushes air to make sound. Electric motors apply the same force on a current-carrying conductor.

• A relay isolates the control circuit from the load.
• A diode across a coil absorbs the voltage spike on switch-off.
• Speakers and motors both use the motor effect.

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