Lenz’s Law

Lenz's law states that when a current is induced in a conductor, the direction of the current will be such that its magnetic effect opposes the change that induced it.

When the bar magnet is pushed towards the ring, the current induced in the ring creates a magnetic field that opposes the change in flux. The magnetic field produced by the induced current repels the incoming magnet.

If we wish to push the magnet towards the ring, we will have to do work on the magnet. This work shows up as electrical energy in the ring. Lenz’s law follows from the law of conservation of energy.

ε = – dφ/dt