AC Generator

An electric generator is used to convert mechanical energy to electrical energy.

Principle: It is based on the principle of electromagnetic induction. It is used to produce electric current by varying magnetic field through a coil.

Parts of Electric Generator: The difference parts of electric generator are explained as below:

1. Armature It is a coil having large number of turns of insulated copper wire wound over a soft iron core.

2. Field Magnet: It is a powerful magnet that provides a uniform magnetic field perpendicular to the axis of rotation of coil between the North and South poles.

3.Slip rings: In an AC generator, we use slip rings that is full rings with which the ends of coil are in contact. DC generator uses split ring type commutator-half rings with which the ends of the armature coil are in contact.

4. Brushes There are two stationary metallic carbon brushes which are in contact with external device and rings.

Types of Electric Generator: Electric generators are of two types:

1. Alternating Current generator (AC generator)

2. Direct Current generator (DC generator)

AC Generator:

It generates the current which changes its direction after equal intervals of time, i.e. alternating current.

Construction: An AC generator consists of a rectangular armature coil (ABCD) placed in a region of strong magnetic field (between the two poles of a permanent magnet). It experiences a torque due to the forces acting on it and produces a current. The two slip rings P and Q maintain contact of the coil with the load resistor through brushes X and Y without resistor being moved.

Working: As the coil rotates, two rings attached with it also rotate . The brushes X and Y keep the contact with the rotating ring P and Q when the coil starts rotating with arm AB moving downwards and CD moving upwards (anti-clockwise) cutting the magnetic lines.

According to Fleming's right hand rule, current is induced in these arms in the direction ABCD. After half rotation, arc CD moves downwards and AB moves upwards. As a result, the direction of current in each segment changes giving rise to net induced current in the direction DCBA. Thus, after every half rotation, polarity of current in the respective arm changes thereby generating an alternating current.

Magnitude of induced emf in a generator can be increased by

1. Increasing the number of turns of armature.

2. Increasing the area of the armature.

3. Increasing the speed of rotation of the armature.

4. Increasing the strength of the magnetic field.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

The Electromotive Force (EMF) developed by the generator depends upon ____________________
A. Area of rotating wire	B. Length of rotating wire	C. Radius of wire	D. Size of magnet
Right Option : D
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Question : 2

If the coil is placed perpendicular to field lines then the number of lines passing through the coil is ________________
A. Minimum	B. Maximum	C. Zero	D. May be maximum or minimum
Right Option : B
View Explanation

Question : 3

In A.C generator increasing the number of turns in the coil , ________________________
A. Decrease the Electromotive force(EMF)	B. Electromotive force(EMF) remains same	C. Increases the electromotive force	D. Electromotive force become zero
Right Option : C
View Explanation