can any please xplain ac generator?

A.C. generators or alternators (as they are usually called) operate on the fundamental principles of electromagnetic induction.

Alternating voltage may be generated by rotating a coil in the magnetic field or by rotating a magnetic field within a stationary coil. The value of the voltage generated depends on-

 the number of turns in the coil.

 strength of the field.

 the speed at which the coil or magnetic field rotates. 

For the derivation of the required formula please refer to the following link:


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in a AC  generator, the electrical power that is produced constantly changes. At first, the generated electric current moves in one direction (as from left to right). Then, when the coil reaches a position where it is parallel to the magnetic lines of force, no current at all is produced. As the coil continues to rotate, it cuts through magnetic lines of force in the opposite direction, and the electrical current generated travels in the opposite direction (as from right to left). The ends of the coil are attached to metal slip rings that collect the electrical current. Each slip ring, in turn, is attached to a metal brush, which transfers the current to an external circuit.

Thus, a spinning coil in a fixed magnetic field will produce an alternating current, one that travels first in one direction and then in the opposite. The rate at which the current switches back and forth is known as its frequency. Ordinary household current alternates at a frequency of 60 times per second (or 60 hertz).

The efficiency of an AC generator can be increased by substituting an armature for the wire coil. An armature consists of a cylinder-shaped iron core with a long piece of wire wrapped around it. The longer the piece of wire, the greater the electrical current that can be generated by the armature.

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Electromagnetic Induction (Physics) Close X
AC Generator

Principle − Based on the phenomenon of electromagnetic induction


M ain parts of an ac generator:

  • Armature − Rectangular coil ABCD

  • Filed Magnets − Two pole pieces of a strong electromagnet

  • Slip Rings − The ends of coil ABCD are connected to two hollow metallic rings R 1 and R 2 .

  • Brushes − B 1 and B 2 are two flexible metal plates or carbon rods. They are fixed and are kept in tight contact with R 1 and R 2 respectively.

Theory and Working − As the armature coil is rotated in the magnetic field, angle θ between the field and normal to the coil changes continuously. Therefore, magnetic flux linked with the coil changes. An emf is induced in the coil. According to Fleming’s right hand rule, current induced in AB is from A to B and it is from C to D in CD. In the external circuit, current flows from B 2 to B 1 .

To calculate the magnitude of emf induced:


A Area of each turn of the coil

N Number of turns in the coil

Strength of magnetic field

θ → Angle which normal to the coil makes with at any instant t

Magnetic flux linked with the coil in this position:

= NBA cos θ = NBA cos ω t …(i)

Where, ‘ ω ’ is angular velocity of the coil

As the coil rotates, angle θ changes. Therefore, magnetic flux Φ linked with the coil changes and hence, an emf is induced in the coil. At this instant t , if e is the emf induced in the coil, then

e = NAB ω sin ω t






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