AC generator
A.C generator is a device which converts mechanical energy into electric energy.
Principle: It works on the principle of electromagnetic induction. It consists of :
(i) Armature coil of a large number of turns of copper wire wound over soft iron core, a soft iron core is used to increase magnetic flux.
(ii) Field magnets are used to apply a magnetic field in which armature coil is rotated with its axis perpendicular to field lines.
(iii) Slip rings used to provide movable contacts of armature coil with an external circuit containing load.
(iv) Brushes are the metallic pieces used to pass on electric current from armature coil to the external circuit containing load.
Theory:
Consider a coil PQRS free to rotate in a uniform magnetic field B. The initial flux through the coil is maximum
i.e., ϕ = BA but as the coil is rotating with angular velocity ω, at any instant 't' the flux is given by
ϕ=BA cosθ =BA cosθ ωt
As the coil rotates, the magnetic flux linked with it changes. An induced emf is set up in the coil which is given by,
Thus, the induced emf varies sinusoidally with time 't'. The value of induced emf is maximum when sin ωt = 1 or at = 90°, i.e., when the plane of the coil parallel to the field vector B Denoting this maximum value by ɛo, we have
As the coil continues to rotate in the same sense the same cycle of changes repeats again and again. Such an emf is called sinusoidal or alternating emf. Both the magnitude and direction of this emf changes regularly with time.
- The fact that an induced emf is set up in a coil when rotated a magnetic field forms the basics principle of a dynamo or a generator.
- The electric current produced varies sinusoidally with time, so is known as alternating current' and hence the generator is known as A.C. generator'.
