Magnetism: Generators and Microphones

Generators

Generators convert mechanical energy into electrical energy using electromagnetic induction.
When a conductor e.g. a coil of wire, moves through a magnetic field, a current is induced in the wire.
The size of the current can be increased by moving the wire more rapidly, using a stronger magnet, or wrapping the wire into more turns.
The direction of the induced current can be reversed by reversing the direction of the movement or the magnetic field, which is demonstrated by the Fleming’s Right Hand Rule.
A simple AC (Alternating Current) generator, also called a dynamo, consists of a coil rotating in a magnetic field, connected to a complete circuit with an external load like a bulb.
The direction of the motion and therefore of the current alternates as the coil rotates through 360°, producing an alternating current.
Commercial generators use multiple coils and slip rings instead of a split ring commutator to produce a smoother AC.

Microphones use the principle of magnetism to convert sound waves into electrical signals.
A typical microphone consists of a diaphragm (a thin piece of flexible material), a coil of wire attached to the back of the diaphragm, and a permanent magnet.
When sound waves strike the diaphragm, they cause it to vibrate. This vibration moves the coil of wire back and forth in the magnetic field of the permanent magnet, inducing a current in the coil.
The size of the induced current corresponds to the loudness of the sound: louder sounds make the diaphragm vibrate more, inducing a larger current.
The frequency of the induced current corresponds to the pitch of the sound: higher pitches make the diaphragm vibrate faster, inducing a current with a higher frequency.
The electrical signal can be amplified and then sent to a speaker, which converts the signal back to sound waves.