A.C. Generator or A.C. Dynamo or Alternator is a device which converts mechanical energy into alternating current (electrical energy).

Principal : A.C. Generator is based on the principle of Electromagnetic Induction.

Construction :

(i) Field Magnet with poles N and S

(ii) Armature (Coil) PQRS

(iii)Slip Rings (R1 and R2)

(iv)Brushes (B1 and B2)

(v) Load

Working : 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 PQRSR_{2}B_{2}B_{1}R_{1}P.

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 PR B_{1}B_{2}R_{2}SRQP.

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.

Theory:

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

E = NBAω sin ωt

E = E0 sin ωt (where E0 = NBAω)