NCERT Solution Class X Science Magnetic Effects of Electric Current Question 16 (Ex 13.9)

Question 16:

Explain the underlying principle and working of an electric generator by drawing

labelled diagram. What is the function of brushes?

Answer:

An electric generator converts mechanical energy into electrical energy.

The principle of working of an electric generator is that when a loop is moved in a

magnetic field, an electric current is induced in the coil. It generates electricity by

rotating a coil in a magnetic field. The following figure shows a simple AC generator.

 

MNST → Rectangular coil

A and B → Brushes

C and D → Two slip rings

X → Axle, G → Galvanometer

If axle Xis rotated clockwise, then the length MN moves upwards while length ST

moves downwards. Since the lengths MN and ST are moving in a magnetic field, a

current will be induced in both of them due to electromagnetic induction. Length

MN is moving upwards and the magnetic field acts from left to right. Hence,

according to Fleming’s right hand rule, the direction of induced current will be

from M to N. Similarly, the direction of induced current in the length ST will be

from S to T.

The direction of current in the coil is MNST. Hence, the galvanometer shows a

deflection in a particular direction. After half a rotation, length MN starts moving

down whereas

length ST starts moving upward. The direction of the induced current in the coil

gets reversed as TSNM. As the direction of current gets reversed after each half

rotation, the produced current is called an alternating current (AC).

To get a unidirectional current, instead of two slip rings, two split rings are used,

as shown in the following figure.

 

In this arrangement, brush A always remains in contact with the length of the coil

that is moving up whereas brush B always remains in contact with the length that

is moving down. The split rings C and D act as a commutator.

The direction of current induced in the coil will be MNST for the first rotation and

TSNM in the second half of the rotation. Hence, a unidirectional current is produced

from the generator called DC generator. The current is called AC current.

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