Connect the terminals of a coil to a sensitive
ammeter or a galvanometer as shown in the figure-14.
Normally, we would not expect any deflections of
needle in the galvanometer because there is to be no
electromotive force in this circuit. Now if we push a
bar magnet towards the coil, with its north pole facing
the coil, a remarkable thing happens. While the magnet is moving towards
the coil, the needle in galvanometer deflects, showing that a current has
been set up in the coil, the galvanometer does not deflect if the magnet
is at rest. If the magnet is moved away from the coil, the needle in the
galvanometer again deflects, but in the opposite direction, which means
that a current is set up in the coil in the opposite direction.If we use the end of south pole of a magnet instead of north pole in the above activity, the experiment works just as described but the deflections are exactly reversed.
Further experimentation enables us to understand that the relative motion of the magnet and coil set up a current in the coil. It makes no difference whether the magnet is moved towards the coil or the coil towards the magnet.
“Whenever there is a continuous change of magnetic flux linked with a closed coil, a current is generated in the coil.”
This is one form of Faraday’s law.
The current generated is called induced current and is set up by an induced electromotive force (induced EMF). This phenomenon of getting induced current is called electromagnetic induction.
Faraday observed that the changes in the magnetic flux through the coil are responsible for the generation of current in the coil. He also observed that the rapid changes in flux through coil generate greater induced current or induced EMF. After observing this important factor, he proposed a law of electromagnetic induction, which is as follow,
“The induced EMF generated in a closed loop is equal to the rate of change of magnetic flux passing through it.”