The dc generator
A direct current (dc) Device that converts kinetic energy into electrical energy. is another device that produces a The potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). This is the voltage between two points that makes an electric current flow between them.. A simple dc generator consists of a coil of wire rotating in a magnetic field. However, it uses a split ring commutator rather than the two slip rings found in alternating current (ac) generators. Some bike lights use a type of dc generator called a An electrical generator which produces direct current, a dc generator. to run the lamps while the wheels are turning.
The dynamo
In a dynamo, a split ring commutator changes the coil connections every half turn. As the induced potential difference is about to change direction, the connections are reversed. This means that the current to the external circuit always flows in the same direction.
Dynamo output on a graph
The output of a rotating dynamo can be shown on a potential difference-time graph. The graph shows a The shape of the graph obtained for y = sin x. The voltage produced by an ac generator follows a sine curve. that stays in the same direction all the time. The maximum potential difference or current can be increased by:
- increasing the rate of rotation
- increasing the strength of the magnetic field
- increasing the number of turns on the coil
The diagram shows four different positions of the coil in a dynamo, and the corresponding potential difference produced.
A - The coil is at 0掳. The coil is moving parallel to the direction of the magnetic field, so no potential difference is induced.
B - The coil is at 90掳. The coil is moving at 90掳 to the direction of the magnetic field, so the induced potential difference is at its maximum.
C - The coil is at 180掳. The coil is moving parallel to the direction of the magnetic field, so no potential difference is induced.
D - The coil is at 270掳. The coil is moving at 90掳 to the direction of the magnetic field, so the induced potential difference is at its maximum. Here, the induced potential difference travels in the same direction as at B.
A - The coil is at 360掳, ie it is back at its starting point, having done a full rotation. The coil is moving parallel to the direction of the magnetic field, so no potential difference is induced.