Describle the construction and working of an AC generator ( an alternator).

Explanation

An electric genertor is a device that converts mechanical energy into electrical energy . Its working is based on electromagnetic induction.

Construction :
(1) Figure 13.30 (a) showns the construction of an AC generator . It consists of a rectangular coil ABCD placed between the two poles of a permgent mganet .
(2) Two ends of this coil are connected to the two metal (copper) rings `R_(1)` and `R_(2)` . The inner side of these rings are insulated .
(3) The two conducting stationary brushed `B_(1)` and `B_(2)` are kept pressed separately on the rings `R_(1)` and `R_(2)` respectively .
(4) The two rings `R_(1)` and `R_(2)` are internally attached to an axle . The axle may be mechanically rotated to from outside to rotate the coil inside the mgnetic field .
(5) Outer ends of the two brushes are connected to the galvanometer to show the flow of current in the given external circuit .
Working :
(1) Suppose, the axle attached to the two rings is rotated such that the arm AB moves up and the arm CD moves down in the magnetic field produced by the permanent magnet . Then the coil ABCD rotates clockwise in the arrangement shown in the figure . By applying Fleming.s right hand rule , we find that the induced currents are set up in thse arms along the direction AB and CD . This means that the current in external circuit flows from brush `B_(2)` to `B_(1)`
[If the coil is made of large number of turns, the current generated in each turn adds up to give a large current through the coil] .
(2) After half a rotation , arm CD starts moving up and AB moving down . As a result , the direction of the induced currents in both the arms change , giving rise to the net induced current in the direction DCBA . This means that the current in the external circuit now flows from brush `B_(1)` to `B_(2)`
(3) Thus , after every half rotation the direction of the current in the respective arms changes.
Such a current , which changes direction after equal interval of time , is called an alternating current (abbreviated as AC).