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What is the process inside an electric generator? - HigherThe ac generator

Electromagnetic induction can create a potential difference. This potential difference causes a current, and the effect is used in electricity generation.

Part of Physics (Single Science)Electric circuits

The ac generator

An (ac) is a device that produces a . A simple ac generator consists of a coil of wire rotating in a magnetic field. Cars use a type of ac generator called an to keep the battery charged and to run the electrical system while the engine is working.

The alternator

The diagram shows a simple alternator.

Current flows in external circuit. Brushes continuous contact between external circuit, slip rings. Slip rings connected to coil. Current induced in rotating coil. The coil rotated in magnetic field.
Slip rings maintain constant contact with the same sides of the coil

As one side of the coil moves up through the magnetic field, a potential difference is induced (created) in one direction. As the rotation continues and that side of the coil moves down, the induced potential difference reverses direction. This means that the alternator produces a current that is constantly changing. This is alternating current or ac.

Alternator output on a graph

The output of an alternator can be represented on a potential difference-time graph, with potential difference on the vertical axis and time on the horizontal axis.

The graph shows an alternating . 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 an alternator, and the corresponding potential difference produced.

An alternator is rotating clockwise. Underneath there is a graph. The curve of the graph is similar to the sine curve.
The potential difference-time graph for an alternator

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 is in the opposite direction to what it was 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.

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Induced potential and the generator effect

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