91Ó°ÊÓ

Whenever a conductor is placed in a varying magnetic field, an electromotive force is induced. The induced emf in a coil is equal to the rate of change of flux linkage.

$\mathrm{Î\mu }=-L\frac{di}{dt}$where $\mathrm{Î\mu }$is induced emf, Lis inductance.

When variable current (i) passes through inductor, an emf is induces according to faraday’s law

$\mathrm{Î\mu }=-L\frac{di}{dt}$.

The point a is at higher potential than b because as the current increases$\frac{di}{dt}$ is positive and induced emf is opposite to flow of current making a at higher potential.

$v_{ab}=L\frac{di}{dt}$.

$v_{ab}=L\frac{di}{dt}$this expression is also correct when I is flowing counterclockwise and decreasing in magnitude because$\frac{di}{dt}$ will be negative but since$v_{ab}$ will be in same direction as in current to support its decrement (as per faraday’s law).

By the same reason,$v_{ab}=L\frac{di}{dt}$ is valid when current is either increasing or decreasing in clockwise direction.

Thus, point a is at higher potential than point b because current increases making the$\frac{di}{dt}$ positive and induced emf directed opposite to current. Also,$v_{ab}=L\frac{di}{dt}$ is valid when current is flowing counterclockwise or clockwise in either increasing or decreasing manner.