What is Lenz's Law?

To determine the direction of induced current, Lenz’s rule is the most convenient method. Lenz’s rule depends on the principle of conservation of energy and Newton’s third law. Lenz’s law states that induced electromotive force with different polarities induces a current whose magnetic field opposes the change in magnetic flux through the loop in order to ensure that original flux is maintained through the loop when current flows in it.

Lenz’s Law

To find the direction of the induced electromotive force and current we look to Lenz’s law. Some experiments were proved by Lenz’s in accordance to his theory:

First Experiment

In the first experiment, he concluded that when the current in the coil flows in the circuit the magnetic field lines are produced. As the current flows through the coil increases, the magnetic flux will increase. The direction of flow of induced current would be such that it opposes when the magnetic flux increases.

Second Experiment

In the second experiment, he concluded that when the current carrying coil is wound on an iron rod with its left end behaving as N-pole and is moved towards the coil S, an induced current will be produced.

In the third experiment, he concluded that when the coil is pulled towards the magnetic flux, the coil linked with it goes on decreasing that means that the area of the coil inside the magnetic field decreases. According to the Lenz’s law, the motion of the coil is opposed when the induced current is applied in the same direction.

To produce current a force is exerted by the magnet in the loop. To oppose the change a force must be exerted by the current on the magnet.

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Practise This Question

A magnet NS is suspended from a spring and while it oscillates, the magnet moves in and out of the coil C. The coil is connected to a galvanometer G. Then as the magnet oscillates,