Question

Draw a neat diagram of an AC generator and explain its working.

Accepted Answer

AC generator converts mechanical energy into electrical energy. It works on the principle of electromagnetic induction. It produces alternating current which changes its direction periodically.

Construction: A simple AC generator essentially consists of the following main parts:

(i) Field magnet: A strong magnet is used to produce an intense magnetic field between its two poles, N and S.

(ii) Armature: A rectangular coil ABCD of many turns placed between the two poles of the field magnet is called armature. It can rotate about its axis of symmetry.

Working: At a certain instant of time, the rectangular coil is in a horizontal plane as shown in the figure. The coil is being rotated by an external agency such that at this instant side AB is moving vertically upwards and side CD is moving vertically downwards. Applying Fleming's right-hand rule we get the direction of induced current. The current flows from D to R₁ to B₂ and then in the external resistance R₂ and galvanometer G from M to N and returns to the rectangular coil form B₁ to R₁ and then from A to B.

At the half rotation i.e., after rotating by $180 °$ , the new position at a particular instant is shown in figure. Here the side DC is moving vertically upwards and the side AB is moving vertically downwards. According to Fleming's right hand rule the direction of induced current is from D to C and from B to A. Thus, current flows from A to R₁ to B₁ and then in the external circuit R_L and galvanometer G from N to M and returns to the rectangular coil from B₂ to R₂ and then to D.

Thus, we see that induced current is from M to N in half rotation of the rectangular coil and from N to M in another half rotation. Thus, the induced current changes its direction after every half rotation. Therefore, we say that alternating current is produced.

Slip rings and brushes : the two ends of the coil are connected to two slip rings R₁ and R₂. These rotate along with the coil. Two carbon brushes B₁ and B₂ are kept in direct contact with the slip rings R₁ and R₂ respectively. The brushes are kept fixed.

When we replace the slip-ring arrangement by split-ring arrangement, an AC generator can be converted into DC generator. The DC generator generates direct current. The split ring converts AC current to DC current.

Substances	Specific heat capacity ( $J {kg}^{- 1} ° C^{- 1}$ )
Water	4200
Oil	2100
Iron	490
Lead	130

Draw a neat diagram of an AC generator and explain its working.

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