Electromagnetic induction

            The generation of electric current in a conductor due to change of magnetic flux through it is called the phenomenon of Electromagnetic induction. The current thus produced is called the induced current and the emf produced is called produced emf.

Faraday’s laws of electromagnetic induction.

          A detailed investigation of magnetic field of induction leads to two laws knows as Faraday’s law, which are state as:

1.      “An emf is induced in a coil through which the magnetic flux is changing. The emf lasts so long as the chang of flux is in progress and becomes zero as soon as the flux through the coil becomes constant.”

2.      “The magnitude of induced emf depends only upon the number of turns and the rate of change of flux linked with the circuit.”

Induced emf = -∆NØ/∆t

Where N is the number of turns of coil, and the –ve sign arises from lenz’s law.

Lenz’s law

                 The direction of induced current was carefully studied by H.E.F lenz a German scientist and the results were generalized most elegantly into a rule in 1835 called lenz’s law. The law states that:

                  “The induced current always flows in such a direction so as to oppose the cause which gives rize to it.”

The cause of the current may be the motion of a conductor in a magnetic field, or it may be the change of flux through a stationary conductor. The current in the moving conductor is such that it posses the motion of the conductor. In the second case the induced current oppose the cause, which is the change of magnetic flux through the circuit. If the original field is increasing, the direction of induced emf will be such that the magnetic field generated by these currents will the original field and vice-versa.

           If we drag a loop of wire leftwards in a uniform magnetic field acting in a downward direction, then the induced current produced in the wire is directed inward on the paper. The force due to this current, as determined by right hand rule is directed rightward, opposite to the dragging force, thereby opposing the cause which has produced it.

Lenz’s law and energy conservation

            Lenz’s law is also directly related with the law of conservation of energy . when we drag the wire across the magnetic field we do work against the magnetic field arising from the interaction of the original magnetic field and that of the induced current and in doing so we impart energy to the loop. This energy is the source of induced current. The electromagnetic induction is exactly according to the law of conservation of energy.