This law is used to find the direction of flow of current due to induced emf. This law was given by a German scientist H.F Emil Lenz which is known as Lenz’s law. It states that, “the direction of induced EMF or induced current is such so to oppose the cause producing it.” Lenz quoted himself about this law as, “this law seems as a son revolting to his father.”
If north pole of the magnet is moved towards the coil so that lines of force passing through the coil increase and hence current is produced in on the coil. According to Lenz law, the direction of induced current opposes the motion of magnet which is shown in figure one 1.A above. It is possible only when current is an anticlockwise direction so that face of the coil towards the magnet behaves like north pole thus tending to oppose the approaching magnet. If the magnet is taken away, the current will be in clockwise direction so that face of the coil behaves as south pole tending to attract the magnet which is shown in Figure 1.B above. Those in both cases the direction of induced current is such that it opposes the motion of the magnet which is lenz’s law.
Lenz's law in accordance with conservation of energy:
When a magnet moves towards or away from a coil, an emf or current is produced in the coil. The induced emf causes induced current to flow in coil in such a way that the magnetic field is produced in the coil due to which the current opposes the magnet towards or away from the coil. Here mechanical energy is applied to move the magnet so that emf is induced i.e. mechanical energy is converted into electrical energy. Due to this induced current, the magnetic field is produced which opposes the magnet. It means electrical energy is converted to magnetic energy which is finally converted to mechanical energy by pushing the magnet. Hence, Lenz’s law is in accordance with the conservation of energy.