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Lenz's Law of Electromagnetic Induction

Lenz's law is named after the German scientist H. F. E. Lenz in 1834. Lenz's law obeys Newton's third law of motion (i.e to every action there is always an equal and opposite reaction) and the conservation of energy (i.e energy may neither be created nor destroyed and therefore the sum of all the energies in the system is a constant).heinrich friedrich emil lenz

Lenz's law is based on Faraday's law of induction, so before understanding Lenz's law ; one should know what is Faraday’s law of induction? When a changing magnetic field is linked with a coil, an emf is induced in it. This change in magnetic field may be caused by changing the magnetic field strength by moving a magnet towards or away from the coil, or moving the coil into or out of the magnetic field as desired. Or in simple words, we can say that the magnitude of the emf induced in the circuit is proportional to the rate of change of flux.

Lenz's Law

Lenz's law states that when an emf is generated by a change in magnetic flux according to Faraday's Law, the polarity of the induced emf is such, that it produces an current that's magnetic field opposes the change which produces it. The negative sign used in Faraday's law of electromagnetic induction, indicates that the induced emf ( ε ) and the change in magnetic flux (δΦB) have opposite signs. Where, ε = Induced emf δΦB = change in magnetic flux N = No of turns in coil

Reason for Opposing, Cause of Induced Current in Lenz's Law?

Explanation of Lenz's Law

For understanding Lenz's law , consider two cases : CASE-I When a magnet is moving towards the coil. When the north pole of the magnet is approaching towards the coil, the magnetic flux linking to the coil increases. According to Faraday's law of electromagnetic induction, when there is change in flux, an emf and hence current is induced in the coil and this current will create its own magnetic field. Now according to Lenz's law , this magnetic field created will oppose its own or we can say opposes the increase in flux through the coil and this is possible only if approaching coil side attains north polarity, as we know similar poles repel each other. Once we know the magnetic polarity of the coil side, we can easily determine the direction of the induced current by applying right hand rule. In this case, the current flows in anticlockwise direction. CASE-II When a magnet is moving away from the coil lenz law When the north pole of the magnet is moving away from the coil, the magnetic flux linking to the coil decreases. According to Faraday's law of electromagnetic induction, an emf and hence current is induced in the coil and this current will create its own magnetic field. Now according to Lenz's law, this magnetic field created will oppose its own or we can say opposes the decrease in flux through the coil and this is possible only if approaching coil side attains south polarity, as we know dissimilar poles attract each other. Once we know the magnetic polarity of the coil side, we can easily determine the direction of the induced current by applying right hand rule. In this case, the current flows in clockwise direction.

NOTE : For finding the directions of magnetic field or current, use right hand thumb rule i.e if the fingers of the right hand are placed around the wire so that the thumb points in the direction of current flow, then the curling of fingers will show the direction of the magnetic field produced by the wire. right hand rule The Lenz law can be summarized as under:

Application of Lenz's Law



SSELVA commented on 12/05/2018
Very good and easy to understand
TTIES commented on 24/02/2018
Very nice explanation
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