6.9 - Alternators
Alternators generate alternating current
- A generator uses movement to induce a current, doing the reverse of a motor.
- An alternator is a generator that produces an alternating current.
How an alternator works
- A coil of wire rotates in a magnetic field, or a magnet rotates inside a coil of wire.
- As the coil (or magnet) turns, it cuts through the magnetic field lines, inducing a potential difference across the ends of the coil.
- If the coil is part of a complete circuit, this drives a current.
- The induced potential difference changes direction every half turn, because each side of the coil reverses the direction it moves through the field.
- The output is an alternating potential difference, which drives an alternating current.
Slip rings and brushes
- An alternator uses slip rings and brushes to keep the output alternating.
- A slip ring is fixed to each end of the coil and rotates with it.
- Each slip ring stays in continuous contact with a brush, which doesn't rotate and connects to the rest of the circuit.
- The brushes stay in contact with the same end of the coil throughout, so the connection is never swapped over.
TermDefinition
GeneratorA device that uses movement to induce a current.
AlternatorA generator that produces an alternating current.
Slip ringA continuous ring fixed to the end of a rotating coil that stays in contact with a brush.
DynamoA generator that produces a direct current.
Split-ring commutatorA split ring that reverses the connections between a rotating coil and the circuit every half turn, which keeps a motor turning one way or makes a dynamo give direct current.
OscilloscopeAn instrument that displays how a potential difference changes with time, as a graph of potential difference against time. It is also called a cathode ray oscilloscope.