Electromagnetic Induction

Electromagnetic Induction

When it was shown by Oersted that magnetic field is produced around a conductor carrying current, the reverse effect was also attempted. In 1831, Michael Faraday explained the possibility of producing an e.m.f across the conductor when the magnetic flux linked with the conductor is changed. In order to demonstrate this Faraday conducted the following experiments.

1. Faraday’s experiments

Experiment 1

In this experiment, two coils were wound on a soft iron ring (separated from each other). The coil on the left is connected to a battery and a switch K. A galvanometer is attached to the coil on the right. When the switch is put ‘on’, at that instant, there is a deflection in the galvanometer. Likewise, when the switch is put ‘off ’, again there is a deflection – but in the opposite direction. This proves the generation of current.

Experiment 2

In this experiment, current (or voltage) is generated by the movement of the magnet in and out of the coil. The greater the number of turns, the higher is the voltage generated.

Experiment 3

In this experiment, the magnet is stationary, but the coil is moved in and out of the magnetic field (indicated by the magnetic lines of force). Here also, current is induced.

All these observations made Faraday to conclude that whenever there is a change in the magnetic flux linked with a closed circuit an emf is produced and the amount of emf induced varies directly as the rate at which the flux changes. This emf is known as induced emf and the phenomenon of producing an induced emf due to change in the magnetic flux linked with a closed circuit is known as electromagnetic induction.

Note:

The direction of the induced current was given by Lenz’s law, which states that the induced current in the coil flows in such a direction as to oppose the change that causes it. The direction of induced current can also be given by another rule called Fleming’s Right Hand Rule.

2. Fleming’s Right Hand Rule

Fleming formulated Right Hand Rule to find the direction of flow of current when a conductor is placed in a changing magnetic field as he formulated Left Hand Rule to find the direction of the force in a current carrying conductor placed in a magnetic field.

Stretch the thumb, fore finger and middle finger of your right hand mutually perpendicular to each other. If the fore finger indicates the direction of magnetic field and the thumb indicates the direction of motion of the conductor, then the middle finger will indicate the direction of induced current. Fleming’s Right hand rule is also called “generator rule”.