Question

explain lenz rule ?

Answer 1

Lenz's law is named after Heinrich Lenz, and it says: An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the change in original magnetic flux.

Answer 2

Lenz’s Law states that the direction of the induced current is such that it opposes the change that has induced it. In other words, it is defined as “Effect Opposes the Cause”.

Lenz’s Law is used to find the direction of induced current in a conducting loop. As perFaraday’s Law of electromagnetic induction, a current is induced in a conducting loop by the changing magnetic flux. This induced current itself produces a magnetic field and hence a magnetic flux. This magnetic flux may have the same sign as the original magnetic flux or may have the opposite sign. It strengthens the original magnetic flux if it has the same sign or weakens it if opposite sign. Here effect is induced current and cause is changing magnetic flux.

Thus, if the current is induced by increasing magnetic flux, it will weaken the original flux. If the current is induced by the decreasing flux, it will strengthen the original flux.

from figure  a magnet is brought toward a circular loop. The North Pole of magnet is facing the loop. As the magnet get closer to the loop, the magnetic field through the loop increases. Due to which, the flux of the magnetic field through the closed loop increases. Mind here that, the cause is increasing magnetic flux and effect is induced current. Therefore as per Lenz’s Law, the effect i.e. induced current shall oppose the cause. Therefore, induced current will produce a magnetic flux which will weaken the original magnetic flux. The direction of original magnetic field is going into the plane of conducting loop. Therefore, the induced current shall produce magnetic field toward the magnet or away from the plane of conducting loop to oppose the cause. Hence, the direction of induced current is anticlockwise by Screw Rule.

The Right side of the Figure shows that the wire AB is sliding toward left. Therefore, the area ABCD decreases with the slide of wire AB. Notice here that magnitude and direction of magnetic field is constant. But as the area ABCD is decreasing, the flux linkage Ø = BA will decrease. Therefore, from Faraday’s Law, a current will be induced in the circuit ABCD.