10th Class Science Magnetic Effects of Electric Current Electric Generator

         Electric Generator

Electric generator is a device which convert mechanical energy into electrical energy. A small generator is called a dynamo which is used in bicycle. It works on the principle of application of electromagnetic induction.-When a straight conductor is moved in a magnetic field, the current is induced in the conductor. It is of two types: alternating current generator and direct current generator. An A.C. generator produces current which reverses its direction continuously after every half cycle. A simple A.C. generator consists of a rectangular coil PQRS which can be rotated rapidly between the poles of the horseshoe magnet as shown in the figure given below.

The coil is made up of large number of turns of insulated copper wire. The two ends P and S of the coil are connected to two circular pieces of copper metal called slip rings \[{{R}_{1}}\]and \[{{R}_{2}}\]. As the slip rings rotate with the coil the two fixed pieces of carbon called carbon brushes X and Y keep contact with them so that the current produced in rotating coil can be carried out through the brushes to the out sources. As the coil rotates between the pole of the magnet in anticlockwise direction, the arm PQ of the coil moves in downward direction cutting the magnetic line of forces near the north pole of the magnet. The arm RS moves in upward direction and cuts the magnetic line of forces near the south pole of the magnet. Due to this the current is induced in the arm PQ and RS of the coil and the current flows in the direction QPSR. After half revolution, the side PQ and RS of the coil interchange their positions. The arm PQ moves in upward direction which earlier moved in the downward direction and vice versa. As a result of this the direction of current in arm PQand RS is reversed giving rise to the net induced current in the direction of RSPQand the current flows through brush X and Y to the outer circuit. In India the A.C. produced is of frequency 50 HZ i.e. the coil is rotted at the rate of 50 revolution per second. In one revolution, the current reverses its direction two times so in 50 revolution of the coil the current reverses its direction 100 times.

The DC generator is the generator in which the current do not changes its direction after every half cycle. The basic difference in construction of AC and DC generator is that, in DC generator slip ring of AC generator is replaced by commutator half ring due to which the current always flows in one direction, through the coil.