Question

Describe the working of an AC generator with the help of a labelled circuit diagram. What changes must be made in the arrangement to convert it to a DC generator?

Answer 1

The labeled diagram of the AC generator is as follows :

The working of the AC generator is as follows:

An electric generator (as shown in the figure above), consists of a rotating rectangular coil ABCD placed between the two poles of a permanent magnet. The two ends of this coil are connected to the two rings R₁ and R₂. The inner side of these rings is made insulated. The two conducting stationary brushes B₁ and B₂ are kept pressed separately on the rings R₁ and R₂, respectively.

The two rings R₁ and R₂ are internally attached to an axle.

The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. Outer ends of the two brushes are connected to the galvanometer to show the flow of current in the given external circuit.

When 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. Let us say the coil ABCD is rotated clockwise in the arrangement shown in the figure. By applying Fleming’s right-hand rule, the induced currents are set up in these arms along the directions AB and CD. Thus an induced current flows in the direction ABCD. This means that the current in the external circuit flows from B₂ to B₁.

After half a rotation, arm CD starts moving up and AB moving down. As a result, the directions of the induced currents in both the arms change, giving rise to the net induced current in the direction DCBA. The current in the external circuit now flows from B₁ to B₂. Thus, after every half rotation, the polarity of the current in the respective arms changes and an alternating current is produced.

To get a direct current a split ring type commutator must be used in place of slip ring type commutator.