In this experiment, Faraday takes a magnet and a coil and connects a galvanometer across the coil. At starting, the magnet is at rest, so there is no deflection in the galvanometer i.e needle of the galvanometer is at the centre or zero position. When the magnet is moved towards the coil, the needle of galvanometer deflects in one direction. When the magnet is held stationary at that position, the needle of galvanometer returns back to zero position. Now when the magnet is moved away from the coil, there is some deflection in the needle but in opposite direction and again when the magnet becomes stationary, at that point with respect to the coil, the needle of the galvanometer returns back to the zero position. Similarly, if the magnet is held stationary and the coil is moved away and towards the magnet, the galvanometer shows deflection in a similar manner. It is also seen that the faster the change in the magnetic field, the greater will be the induced emf or voltage in the coil.This induced emf when applied across the resistor, current will flow through the circuit.
Due to the movement of the magnet, there is a change in the magnetic flux in the coil as no. of magnetic field lines passing through the coil changes due to movement of the magnet. This change in magnetic flux produces emf or voltage in the coil, due to which deflection occurs in the galvanometer. The direction in which the needle deflect will tell us in which direction magnet is moving. ( towards the coil or away from coil )
As magnet moves, You can see the number of magnetic field lines passing through the coil changes, hence magnetic flux changes. Due to change in magnetic flux, EMF is induced. Due to induced EMF, there is a deflection in the galvanometer.
Magnetic flux is the number of magnetic field lines passing through the coil.
Emf in the coil is induced to resist the change in the magnetic flux, which is caused by the movement of the magnet or coil. If the magnetic flux is increased by the movement of the magnet then the direction in which the emf is induced in coil is such that it decreases the magnetic flux as coil wants to resist the change in magnetic flux and if the magnetic flux is decreased than the direction of the emf induced will be such that it increases the magnetic flux.
Emf is induced to resist the change in the magnetic flux and if there is no change in the magnetic flux than zero emf is induced, which means galvanometer will show no deflection. When the magnet is at rest, the magnetic field lines which are passing through the coil will remain constant and the magnetic flux will remain constant. Hence, no emf will be induced in the coil.