Lenz Law

In 1834 Russian PhysiclstHelnrich Lenz Found that the polarity
of induced emf always leads to an induced current that oppose
the change which induces emf.

statement:

The direction of indues current is always such as to oppose the change which causes the current.

Condition For Its Application:

we can apply Lenz law directly to closed loop because is refers to induced currents and not to induced emf.however if the loop is not closed, we imagine as if it is closed and then from the direction od induced current, we can find the polarity of induced emf.

Explanation:

                       As current carrying coll behaves as a bar magnet due to the magnetic effect of current. One face of the coll acts as the north pole while the other one as the south pole. Then by Lenz Law, if the coil is to oppose the motion of bar magnet then the face of the coil wards the magnet must become a north pole, as shown in the figure. The two north poles repel each other. By right-hand role, The induced current must be in anti-clockwise direction from the side of bar magnet.

According to Lenz Law the push of magnet is the change which produces the induced current which tends to oppose push. similarly, if we pull the magnet away from the coil, the induced current oppose the pull by creating the south pole towards the bar magnet.

Lenz law of Conservation of Energy

Let us consider the experimental arrangment in which a rod of lenth L is placed on a conducting rail as shown in figure.

Force acting on rod when it moves to ringht

when the rod moves towards ringht, emf is induced in it and induced current flows through the loop in anti-clockwise direction. Now the rod becomes a current carrying conductor moving in the magnetic field, so it experiences a force given by,

According to ringht hand role, the direction of f is opposite to v. so, it tends to stop the rod, as shown in fingure.