priyanka jakhar

1. AC Generator
Class -12th
PRIYANKA JAKHAR
PHYSICS LECTURER
GGIC VIJAY NAGAR
GHAZIABAD

2. AC Generator:
AC generator is the one which produces a current that alternates or changes its
direction regularly after a fixed interval of time, i.e., it is a device which converts
mechanical energy into the alternating form of electrical energy.
The principle of AC Generator:
It is based on the phenomenon of electromagnetic induction–when the coil is
rotated with a constant angular velocity W in a uniform magnetic field B, then the
magnetic flux linked with the coil changes and an alternating current is induced in
the coil.
AC Generator DC Generator

3. Construction of AC Generator:
(1) Armature: It is a coil of large no. of turns of copper wire wound over an iron
core. (because iron has high permeability). The coil is rotated about its axis.
(2) Field Magnets: North and south are the pole pieces of a strong magnet in
which the coil is rotated. The axis of the coil is perpendicular to the magnetic field.
(3) Rings (R1 and R2): (also called slip rings): These are the two hollow metallic
rings which are connected to the ends of the coil. These rings rotate with the
rotation of coil. Slip rings helps in electrical contact with the brushes.It does not change current
direction.
•The slip rings provide a continuous connectionwith the wire around the armature.
•These slip rings are attached to carbon brushes.
(4) Brushes (B1 and B2): These are the two metal plates or carbon rods. They are
fixed and kept in contact with R1 and R2. The purpose of the brushes is to pass
current from the armature to the external load resistance.
(5) Axle :The rectangular coil is capable of rotating about an axis which is perpendicular to the
magnetic field.
•The axis of rotation is known as axle.
(6) Coil -- which is tied over a soft iron core, soft iron increase the magnetic flux passing through the

4. Cycle---- variation of alternating current or voltage between zero to maximum and then to
zero (+ve) and than in opposite direction (-ve) zero to maximum and again to zero is known as
cycle .
Each cycle has two symmetrical half parts
positive half cycle
negative half cycle
•Period: – This is the length of time in seconds that the waveform takes to repeat itself from start to finish. This value
can also be called the Periodic Time, ( T ) of the waveform for sine waves, or the Pulse Width for square waves.
•Frequency: – This is the number of times the waveform repeats itself within a one second time period. Frequency is
the reciprocal of the time period, ( ƒ = 1/T ) with the standard unit of frequency being the Hertz, (Hz).
•Amplitude: – This is the magnitude or intensity of the signal waveform measured in volts or amps.
•a sinusodial wave can be represented in the form of sin function whereas we cannot express the
non-sinusodial wave in terms of sine function.
Non-sinusoidal waveforms are waveforms that are not pure sine waves. They are usually derived
from simple math functions. While a pure sine consists of a single frequency, non-sinusoidal
waveforms can be described as containing multiple sine waves of different frequencies. These
"component" sine waves will be whole number multiples of a fundamental or "lowest" frequency.

5. Theory of Working of AC Generator:
Suppose that the plane of the coil is such that its axis is perpendicular to the
magnetic field.
As the coil is rotated clockwise, the side AB of the coil moves upward and the
other side CD moves downwards. The flux in the coil changes, the current is
induced, the direction of the current in the side AB will be outward according to
Fleming’s right-hand rule.
In the next half cycle, AB moves downward and CD moves upward. Now, the
direction of current induced in AB is inward according to Fleming’s right-hand
rule.

6. Let the armature be rotated in such a
way that the arm PQ goes down and
RS comes up from the plane of the
diagram. Induced emf and hence
current is set up in the coil. By
Fleming’s Right Hand Rule, the
direction of the current is
PQRSR2B2B1R1P.
After half the rotation of the coil, the
arm PQ comes up and RS goes down
into the plane of the diagram. By
Fleming’s Right Hand Rule, the
direction of the current is
PR1B1B2R2SRQP.If one way of current
is taken +ve, then the reverse current
is taken –ve.
Therefore the current is said to be
alternating and the corresponding
wave is sinusoidal.
A.C. Generator:
A.C. Generator or A.C. Dynamo or Alternator is a device which converts
mechanical energy into alternating current (electrical energy).
R1
R2
B1
B2
Load
R1
R2
B1
B2
Load

8. Thus, alternating current is induced in the coil in one complete cycle which flows
from the brushes B1 and B2 to the external load resistance such that an alternating
voltage is developed across RL.
Φ = N B A cos θ
At time t, with angular velocity ω,
θ = ωt (at t = 0, loop is assumed to be
perpendicular to the magnetic field and θ = 0°)
Φ = N B A cos ωt
Differentiating w.r.t. t,
𝒅𝜱
𝒅𝒕
= - NBAω sin ωt
E = - dΦ / dt
The induced emf produced by the AC generator is given by
E = NBAω sin ωt
E = E0 sin ωt (where E0 = NBAω)
0
π 2π 3π 4π
T/4 T/2 3T/4 T 5T/4 3T/2 7T/4 2T
t
π/2 3π/2 5π/2 7π/2 θ = ωt
E0
P
Q
R
S
B
θ
ω
n

9. These day production of electricity in electrical plants is based on the principle. Armature is
connected to turbine and rotate with it only . Turbine has a rotator fitted with blades .In some
plants to ,rotate the turbine required energy is obtained by falling water from height for
example by dams. They are known as hydroelectric generator.
In thermal generator, heat is generated by heating the water and connected into steam using
coil or other sources. This steam rotates the turbine blades with high pressure.In place of coil if
nuclear fuel is used then we get nuclear energy .Modern plants can generate power up to 500
Mega Watt. 50 lacs bulb of hundred watt can be lighted simultaneously.
In modern generators Kola capital stationary and the magnet is rotated.
In India rotation frequency of generator is 50 hertz whereas in America this is 60 Hertz .