FARADAY’S DYNAMOMichael Faraday devised the world’s first electric generator in 1821. The generator he built was a seemingly simple thing: a hand-cranked copper disk rotated between the poles of a permanent magnet.

THIS IS HOW FARADAYS GENERATOR OR DYNAMO WORKS

DC GENERATORS Are used in recharging automobile

batteries. A direct-current (DC) generator is

a rotating machine that supplies an electrical output with unidirectional voltage and current.

The field is produced by direct current in field coils or by permanent magnets on the stator. The output, or armature, windings are placed in slots in the cylindrical iron rotor.

The current / vs time t graph for a single coil DC generator

(a) Cross sectional view of a single coil generator

(b) The pulsating DC from a single-coil generator

Possible positions of the single-loop DC generator in the magnetic field showing the direction of the current in the loop and in the external circuit.

(a) Profile of a three-coil DC generator.

(b) The voltage-time graph for the three-coil DC generator.

AC GENERATORS Are used in electric power plants. An AC generator is an electric

device that produces an alternating current, which is electric current that reverses direction several times every second. Such generators are also known as synchronous generators or alternators.

(a)A simple AC generator.(b) A graph showing current at different

positions of the loop.

-At position P, the current in the circuit connected to the loop is counterclockwise.

- At position R, the current in the circuit connected to the loop is clockwise.

The direction of AC reverses every half cycle.

MOTORS AND GENERATORS Compare the illustrations of a dynamo and a DC

motor. The action of the dynamo is just the reverse of the action of a motor,

The similarity between these two was not recognized until the mid-nineteenth century when an “accident” happened at the Vienna Exposition Hall in 1873.

The 2nd dynamo began to spark and whine and come live. The dynamo had become a generator.

The versatility of a device to act as a motor at one time and a generator at other times can be used to great advantage.

In France and Australia, trains running uphill or on level ground are fueled by electricity from power lines. When the train moves downhill, however, its motor becomes a generator. The power generated is sent to the power lines to be used by other trains. This maintains a cycle of changes from gravitational potential energy to electrical energy.