An electric device which converts mechanical energy into electric energy
is called an electric generator.
Principle: Electric generator works on the
principle of electromagnetic induction. When the coil of electric generator
rotates in a magnetic field, the magnetic field induces a current in this coil.
This induced current then flows into the circuit connected to the coil.
Types of electric generators:
1. AC Generator
2. DC Generator
1. AC Generator: A generator
which converts mechanical energy into electric energy in the form of alternating
current is called AC Generator.
Construction:
The main components of AC generator are as shown in
figure.
1. Armature 2. Strong magnets 3. Slip rings and 4. Brushes.
Armature,
strong magnets and brushes are the same as used for electric motors.
Slip rings:
The two ends of the armature coil are connected to two
brass slip rings R1 and R2. These rings rotate along with the armature coil.
Working:
a.
When the armature coil ABCD rotates in the magnetic field provided by
the strong magnets, it cuts the magnetic lines of forces.
b. Thus the changing magnetic field produces induced
current in the coil. The direction of induced current is determined by the
Flemings right hand rule.
c.
The current
flows out through the brush B1 in one direction in the first half of the
revolution and through the brush B2 in the next half revolution in the reverse
direction, this process is repeated.
d. Therefore, the induced current produced is of
alternating nature. Such a current is called as alternating current.
2. DC Generator:
A generator
which converts mechanical energy into electrical energy in the form of direct
current is called as DC generator.
Construction:
The main components of D.C. generator are:
1.
Armature coil 2. Strong magnets 3. Split rings or commutator 4. Brushes
5. Bulb.
The components such as armature coil, strong magnet, brushes are the same
which are used for AC generators. Slip rings or commutator is the same as used
in electric motor.
Working of DC generator:
(a)
When the coil of DC generator rotates in the
magnetic field, potential difference is produced in the coil. This gives rise
to the flow of current. This is shown by glowing of the bulb.
(b)
In D.C. generator, the flow of current in the
circuit is in the same direction as long as the coil rotates in the magnetic
field.
(c)
This is because one brush is always in contact with
the arm of the armature moving up and other brush is in contact with the arm of
the armature moving downward in the magnetic field.
