An electric generator converts mechanical energy into electrical energy. Alternating current generator's or AC generators produce alternating current.
Principle: lt works on the principle of electromagnetic induction.Whenever the magnetic flux through coil changes, the induced current is produced.
Construction: Alternating current generator consists of a rectangular coil ABCD called armature. The armature coil consists of a large number of turns of insulated copper wire bound over a soft iron core. The coil is kept between the poles of a strong magnet. In the figure shown R1 and R2 are two slip rings connected to the two ends of the coil and convey the current produced to outside circuit. B1 and B2 are two carbon brushes remain in sliding contact with slip rings.
Working : The coil of the generator is rotated with the help of an axel. When coil rotates, it cuts the magnetic lines of force (magnetic field) near the north (N) and south (S) poles of the magnet. By electromagnetic induction, a current is induced in
the coil. The direction of this current- is given by Fleming's right-hand rule. As this coil turns clockwise, arm AB moves up and arm CD goes dorvn. the direction of current is from A to B in AB and C to D in CD. The induced current is taken out through, slip rings and carbon brushes. After half this rotation, AB and CD interchange their position. Non'CD moves upward and AB downward. the direction of induced current is from D to C in CD and B to A in AB, during this half rotation. The slip rings R1 and R2 also rotate along with the coil ABCD. Thus, their polarities keep changing after every half rotation. Thus, the current changes its direction twice in one complete revolution of the coil. Such a current which changes its polarity after fixed intervals is called alternating current.
Function of Brushes: The brushes B1 and B2 remain fixed in their positions and maintain sliding contacts with the rotatable slip ring R1 and R2 respectively. It is through these brushes that the current induced in the armature coil is fed to the external circuit by means of line wires.