Electrical Engineering ⇒ Topic : Generation of Induced E.M.F. and Current

GENERATION OF INDUCED E.M.F. AND CURRENT

Figure (a) shows an insulated coil whose terminals are connected to a sensitive galvanometer G.There is a bar magnet AB close to the coil. When the bar magnet is suddenly moved towards the coil in position A'B', there is a deflection in the galvanometer. This deflection in galvanometer lasts so long as there is relative motions of the magnet with respect to the coil, i.e., with respect to the flux linking with the coil changes.

                                                                                  FIGURE (A)

Figure (B) shows that when the magnet is withdrawn, the deflection of the galvanometer is in opposite direction to the aforementioned case. This deflection exists so long as the bar magnet is in relative motion to the coil, i.e., the flux linking with the coil changes.

                                                                                 FIGURE (B)

In both the cases the deflection is reduced to zero when the bar magnet becomes stationary.The flux linked with the coil is increased as the bar magnet approaches the coil in the first case while in the second case the flux linked with the coil is decreased due to withdrawal of the bar magnet.

It is clear that the deflections in two cases are in different directions. The deflection in galvanometer shows that there is an induced current produced in the coil. In the first case, theinduced current flows through the coil in anti-clockwise direction as seen from the bar magnet.This indicates that the face of the coil is N pole. To move the bar magnet towards the coil, the force from outside must be given to the coil. When the magnet is withdrawn, the current flows in clockwise direction as seen from the bar magnet. This indicates that the face of the coil is S pole.So once again force must be supplied to the coil from outside to take it away from the bar magnet. Here the principle of conservation of energy is fully satisfied.

From the above mentioned results, Faraday had proposed two laws which are discussed below.