What is Lenz’s Law

What is Lenz’s Law .Lenz’s Law was deduced in 1834 by Russian Physicist name Heinrich Lenz(1804-1865) and according to Lenz’s Law “The direction of current in a conductor by changing magnetic field  (according to Faraday Law of induction)is such that the magnetic field  created by the induced current opposes the initial changing magnetic field which produced it.”

The direction of that current which produced by it is given by Fleming;s right hand rule.

Lenz’s Law is based on Faraday Law of induction .Faraday Law tell us about ,the changing magnetic field will induced a current in a conductor .

Lenz’s Law tell us the direction of that induced current which opposes the initial changing magnetic field which produced it

This is signified in the formula Faraday ‘s Law by the negative sign ( “ – “ )

Formula for Lenz’s Law

Lenz’s Law Explanation

To understand lenz;s law consider two cases

Case 1:

When a magnet is moving toward the coil .

If the north pole of the magnet is approaching toward the coil,the magnetic flux linking to the coil increases.

According to the Faraday Law of electromagnetic induction there will be change in flux, an emf and hence current is induced in the coiland this current create its own ,magnetic field

According to Lenz’s Law this created magnetic field will oppose its own or we can say that this magnetic field oppose the increase in flux through the coil and this is possible only when approaching coil side attains north polarity, as we know similar poles repel each other .

If we know the magnetic polarity of coil side ,we can easily  determine the direction of induced current by applying  Fleming right hand rule .

In this case the current flows anticlockwise direction.

Case NO 2

When  magnet is moving beyond  the coil

When  north pole of the magnet is moving beyond the coil, the magnetic flux linking to the coil decrease.

Faraday’s law said 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 created magnetic field 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 ,so as we know that dissimilar poles attract each other.

Once we know the magnetic field of the coil we can find the direction of induced emf by using right hand rule.

According to Right hand rule to find the direction of induced emf ,if the finger of the right hand are placed around the wire so that the thumb points in the direction of current flow, then curling of fingers will show the direction of the magnetic field produced by wire

In this cases Lenz’s Law stated as

• If the magnetic flux linking the coil increase,the direction of current in the coil will be such that it will oppose the increase in flux and hence the induced current will produce its flux in the direction according to the Fleming’s right hand rule
• If magnetic flux linking a coil decrease,the flux produced by the current in the coil is such that it will aid the main flux and hence the direction of current is given by Fleming’s right hand rule

Application of Lenz’s Law

• Lenz’s law is used to understand the concept of stored energy in  inductor.

When a source of emf is connected with inductor ,current will start flowing through it.The back emf will oppose this increase in current through the inductor.

In order to establish the flow of current ,te external source of emf has to do some work to overcome this opposition.

The work which is done by the emf is stored in the inductor and it can be recovered after removing the external source of emf from the circuit

• Len’z law tell us that the induced emf and the change in flux have opposite signs which provide a physical interpretation of the choice of sign in Faraday’s law of induction.
• Lenz’s law is applied to electrical Generator .Its also provide back emf in case of electrical motors
• Lenz’s law is used in electromagnetic braking and induction cooktops.