Electricity Generation

Electricity can be generated by rotating a coil of wire in a magnetic field or by rotating a magnet inside a coil of wire. This is how a generator works.

If a wire, or coil of wire 'cuts through' a magnetic field, or vice-versa, a voltage (potential difference) is produced between the ends of the wire. This induced voltage causes a current to flow if the wire is part of a complete circuit.

The size of the induced voltage increases when:

the speed of the movement increases;
the strength of the magnetic field is increased;
the number of turns on the coil is increased;
the area of the coil is greater.

The Dynamo

A dynamo consists of a magnet which is forced to rotate close to a coil. The repeated motion of the poles past the ends of the coil induces an alternating voltage across the coil. The faster the magnet spins, the higher the induced voltage and the higher the frequency

Graphs of output voltage for different speeds

The A.C. Generator

The current in the coil is always induced in the same direction relative to the magnet, but reverses in the coil as is turns 180°. The slip ring commutator mean each side of the coil is always connected to the 'same side of the circuit'. Therefore Alternating current is provided to the circuit

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A Power Station Alternator

A power station alternator uses an electromagnet instead of a permanent magnet in its rotor. There are 3 separate pairs of coils on the stator. An AC current is induced in each.

Because the coils are 60° apart from each other the 3 currents are out of sync with each other. Devices that require high power or smooth supply use 3 phases. Circuits in homes only use one of the three phases.