## Electromagnetic Induction

### Faraday’s Law of Electromagnetic Induction

The principle of electromagnetic induction was discovered by Michael Faraday in 1831. He stated that a voltage will be generated across a length of wire, if it was exposed to a perpendicular magnetic field flux of changing intensity. Consider a magnet with its lines of force extending from the North to the South Pole, as shown in the following figure.

FIGURE

A conductor is connected to a galvanometer to indicate the presence of emf (electromotive force). The reading shows zero when the conductor is not moving and the pointer deflects when it is moved. This indicates that an emf was induced in the conductor because no lines of force are being cut. So, there must be virtual motion between the conductor and the lines of force in order to induce an emf. The magnet is moved to a coil of wire in order to create a magnetic field. The voltage will be induced only when the magnetic field increases or decreases in intensity perpendicular to the wire.

The formula for calculating the value of induced voltage is given below.

e = induced voltage (V)

N = number of turns in a coil

Φ = magnetic flux (Wb)

t = time (seconds)

dΦ/dt = rate at which the flux cuts across the conductor (Wb/s)

### Lenz’s Law of Electromagnetic Induction

This law is based on Faraday’s law and states that when an emf is generated by a change in magnetic flux, the polarity of the induced emf is such that it produces a current whose magnetic field opposes the change which produces it. The induced magnetic field inside any loop of wire keeps the magnetic flux in the loop constant. If the external field decreases, the conductor magnetic field of the induced current will be in the same direction, thus sustaining the electric field. And if the external field increases, the induced field acts in opposition to it.