Monday, May 27, 2013

It is well known that whenever an electric current flows through a conductor, a magnetic field is generated around the conductor. And the converse of this is also true i.e. when a magnetic field around a conductor moves relative to the conductor, it produce a flow of electrons in the conductor. This phenomenon whereby an emf and hence current is induce in any conductor is cut by a magnetic flux is known as electromagnetic induction.

“Whenever the magnetic flux passing through a circuit or a conductor changes, an emf is induced in the circuit or conductor”
In other words, whenever a conductor cuts the magnetic flux, an emf is induced in that conductor.

“The magnitude of induced emf is equal to the rate of change of magnetic flux linkage.”

Let us consider the magnetic flux of a coil having N turns changes from its initial value Ф1 webers to a final value Ф2 webers in t seconds. Then, remembering that by flux-linkage meant the product of number of turns by the flux linked with the coil, we have:

Initial flux linkages = N Ф1 and final flux linkage = NФ2

Putting the above expression in the differential form, we get:

Usually, a minus sign is given to the right-hand side of expression to signify the fact that the induced emf set up current in such a direction that magnitic field produce by it oppose the very cause producing it (Lenz’s Law).

Lenz’s law states that “the direction of induced emf or current is such that it oppose the very cause producing it.”