Lenz's Law of Electromagnetic Induction

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Lenz's Law 

Lenz's Law of Electromagnetic Induction Image

Lenz's law, named after the physicist Emil Lenz who formulated it in 1834. The direction of the induced current may also be found by this law which was formulated by Lenz* in 1835. This law states, in effect, that electromagnetically induced current always flows in such direction that the action of the magnetic field set up by it tends to oppose the very cause which produces it. This statement will be clarified with reference to Fig. (a) and (b) It is found that when N-pole of the bar magnet approaches the coil, the 
Principal of Lenz's Law Image
  
Principal of Lenz's Law Image

induced current set up by induced e.m.f. flows in the anti- clockwise direction in the coil as seen from the magnet side. The result is that face of the coil becomes a N-pole and so tends to oppose the onward approach of the N-Pole of the magnet (like poles repel each other). The mechanical energy spent in overcoming this repulsive force is converted into electrical energy which appears in the coil. When the magnet is withdrawn as in (Fig.b), the induced current flows in the clockwise

Principal of Lenz's Law Image

direction thus making the face of the coil (facing the magnet) a S-pole. Therefore, the N-pole of the magnet has to withdrawn against this attractive force of the S-pole of coil. Again, the mechanical energy required to overcome this force of attraction is converted into electric energy. It can be shown that Lenz’s law is a direct consequence of Law of Conservation of Energy. Imagine for a moment that when N-pole of the magnet (Fig.a) approaches the coil, induced current flows in such a direction as to make the coil face a S-pole. Then, due to inherent attraction between unlike poles, the

Principal of Lenz's Law Image

magnet would be automatically pulled towards the coil without the expenditure of any mechanical energy. It means that we would be able to create electric energy out of nothing, which is denied by the inviolable Law of Conservation of Energy. In fact, to maintain the sanctity of this law, it is imperative for the induced current to flow in such a direction that the magnetic effect produced by it tends to oppose the very cause which produces it. In the present case, it is relative motion of the magnet with magnet with respect to the coil which is the cause of the production of the induced current. Hence, the induced current always flows in such a direction to oppose this relative motion i.e., the approach or withdrawal of the magnet.




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