Mains electricity is produced using the process of electromagnetic induction.
When a magnet is moving into a coil of wire a potential difference is induced across the ends of the coil; if the magnet is moving out of the coil, or the other pole of the magnet is moving into it, there is a potential difference induced in the opposite direction.
If the ends of the coil are connected to make a closed circuit, a current will flow round the circuit.
In a moving coil microphone sound waves cause a diaphragm to vibrate.
The diaphragm is attached to a coil which is in the field of a permanent magnet.
Sounds make the coil vibrate, inducing a changing potential difference across the ends of the coil.
This potential difference drives a changing current in an electric circuit.
In a generator, a magnet or electromagnet is rotated within a coil of wire to induce a voltage across the ends of the coil.
The induced voltage across the coil of an alternating current (a.c.) generator (and hence the current in an external circuit) changes during each revolution of the magnet or electromagnet.
To generate a d.c. split-ring commutator is used so that the current always passes from the same side of the generator. |
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