Draw a labeled diagram of an a.c generator. Explain briefly its principle and working.

Principle: It works on the principle of Faraday’s law of electromagnetic induction. Whenever a coil is rotated in a uniform magnetic field about an axis perpendicular to the field, the magnetic flux linked with coil changes and an induced emf is set up across its ends.


The essential parts of an ac generator are shown in the figure. Initially, the armature coil ABCD is horizontal. As the coil is rotated clockwise, the arm AB moves up and CD moves down.

The magnetic flux linked with the coil at any instant is:
Φ =  NBAcosωt
Induced emf will be
E= – dΦ/dt
=- d/dt (NBA cos ωt) = NBA ω sin ωt
Let Eo  be the peak value of induced emf,
E = Eo sin ωt
where, Eo = NBA ω

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