A.C. Generator is a device which is used to convert the mechanical energy in to electrical energy is called electric generator.
It is based on the principle of electro magnetic induction. When a coil rotated about on axis perpendicular to the direction of uniform magnetic field, an induced e.m.f. is produced across it.
The A.C. Generator is consist of four main parts :
(1) The coil (Armature) :
A rectangular coil ABCD consist of a large number of turns of copper bound over a soft iron core is called armature. The soft iron core is used to increase the magnetic flux.
(2) Magnetic Field :
It is usually a permanent sponge magnet having concave poles. The armature is rotated of a magnet so that axis of the armature is perpendicular to magnetic field lines.
(3) Slip Rings :
Slip rings are the magnetic rings which are connected in the terminal of the armature. These rings are rotated with the coil and these are use to draw the current from the generator.
(4) Brushes :
The brushes B1 & B2 are just touch the slip rings. They are not rotating with the coil and these brushes leads to the output of load resistance.
The coil is rotated in anti-clock wide direction. In the first half rotation the arm AB is moving outward and CD is moving inward. So the e.m.f. is induced in the arm AB from A to B. And in the arm CD from C to D. After half rotation (in the second half). The arm CD is moving outward and AB is moving inward. In this time current is induced in arm CD from D to C. And in arm AB from B to A. In the second half rotation the current direction is changing so in this generator AC is produced.
Let position of the coil at any time t. It's make angle q an angle with vertical. If w is uniform angular speed of the coil.
Then q = wt
B be the strength of magnetic field n be the number of turns in the coil and A area of the coil then magnetic flux with the coil in this position is given by :
f = nBA Cos q = nBA Cos wt.
differentiate w.r.t. time.
= nBA (-Sin wt) w
= -nBA w Sin wt
e = = -(-nBA w Sin wt)
maximum value of e.m.f. say e0
e = e0 Sin wt.