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Lenz's law














What is Lenz's law?

 An electric current induced by a changing magnetic field will flow such that it will create its own magnetic field that opposes the magnetic field that created it.

 Lenz's law is sometimes similar to the Faraday's law in that both laws discuss about induction. However, Lenz's law clearly demonstrates the direction of the induced current as opposed to the theoretical observation by the Faraday's law.

 To understand Lenz's law, consider the system below:


(Photo credit: www.pinkmonkey.com)

Before explaining this system using Lenz's law, let us remind about the direction of the field lines around the magnet.














Now let us consider the above system in detail.

 Consider Fig 1(a):
















When the north pole is brought close to the magnet, the field lines will be as follows: 














As Lenz's law states 'an electric current induced by a changing magnetic field will flow such that it will create its own magnetic field that opposes the magnetic field that created it' , the direction of the induced current will be in the opposite direction to the direction of the field lines.

 Thus, the induced current will be counterclockwise or anticlockwise in direction and hence will make a North pole on the coil.

 Consider Fig 1(b):

When the south pole of the magnet is moved away from the loop, the field lines will be as follows:





According to Lenz's law, 'an electric current induced by a changing magnetic field will flow such that it will create its own magnetic field that opposes the magnetic field that created it' .

 Thus as described in the previous situation, the direction of the induced current will be so as to oppose the motion of the magnet. This will result in the creation of a south pole in the loop.

 The instances 1(c) and 1(d) can be explained similarly.
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