Name: Production of Induced EMF by Rotating the Loop
Uploaded: 2019-07-19
Duration: 13 min 16 s
Description: Learn how the magnetic flux can be altered by rotating a coil in a magnetic field such that the angle between the magnetic field and the area vector changes.

Question

Give the principle of construction and working of an a.c. generator. How is it converted to a d.c. generator.

Accepted Answer

When a straight conductor is moved rapidly in a magnetic field, then a current is induced in the conductor. It is based on the phenomenon of electromagnetic induction

An AC generator consists of a magnet with concave cylindrical poles, an armature, and a current collecting arrangement. The current collecting arrangement consists of slip rings and brushes as follows:

Armature is a soft iron core on which a coil having many turns of insulated copper wire is wound. Magnetic poles are concave and cylindrical. The concave poles produce a radial magnetic field.

The ends of the armature are connected to two slip rings. They rotate along with the coil. The slip rings are made of metal and are insulated from each other. There are two brushes $B_{1}$ and $B_{2}$ made of carbon.

One end of each brush is in contact with the rotating slip rings and the other end is connected to an external circuit. The brushes are connected to a galvanometer and brushes do not rotate with the coil. The axle is rotated mechanically from outside by a diesel engine, flowing water, steam or high-speed wind.

Working of AC Generator : As the armature rotates about an axis perpendicular to the magnetic field, it keeps on changing its relative orientation with respect to the field. Thus, the flux keeps on changing continuously with time. This change in magnetic flux induces an emf. If the outer terminals of the armature are connected to an external circuit, an electric current flows through it. The deflection of the galvanometer needle indicates that an emf is induced. The direction of the induced emf is reversed after every half rotation of the coil. Thus, in one rotation of the coil, the current changes its direction twice. Such a current which changes its direction after equal intervals of time is called alternating current (AC). The rotation of the coil at different angles with respect to the field can be visualised as:

To get a direct current (DC) generator from (AC) generator: a split-ring type commutator must be used. In this arrangement, one brush is at all times in contact with the arm moving up in the field while the other is in contact with the arm moving down. Thus, a unidirectional current is produced in such a generator.

Give the principle of construction and working of an a.c. generator. How is it converted to a d.c. generator.

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