Faraday’s Law And Lenz’s Law Of Electromagnetic Induction

In 1831, Micheal Faraday formulated two important laws on the basis of certain experiments that shows a relationship between the electric circuit and magnetic field. These laws are called Faraday’s laws of electromagnetic induction.

Contents

According to Faraday’s First Law, Whenever a conductor is placed in a varying magnetic field, an EMF is induced across the conductor (which is called an induced emf). If the conductor is made a closed circuit then induced current flows through the conductor.

There are various methods that are used to vary Magnetic field such as

1. By moving the coil
2. By moving magnet
3. By rotating the coil relative to magnetic field

According to Faraday’s second law,  the magnitude of induced emf in the conductor is equal to the rate of change of flux linkages with the coil. The flux linkages are the product of a number of turns and the flux associated with the coil.

Consider a conductor which is moving in magnetic field, then

flux linkage with the coil at an initial position of the conductor = NΦ1  Wb
(N is speed of the motor and Φ is flux)

flux linkage with the coil at the final position of the conductor = NΦ2   Wb

then, change in the flux linkage from initial to final = N(Φ1 – Φ2)

let  Φ1 – Φ2 = Φ

therefore, the change in the flux linkage = NΦ

and, a rate of change in the flux linkage = NΦ/t

by taking the derivative of RHS

the rate of change of flux linkages = N (dΦ/dt)

According to Faraday’s second law, the rate of change of flux linkages is equal to the induced emf

So, E = N (dΦ/dt)    (volts)

Phenomenon Of Mutual Induction

When the alternating current flows in the coil, a magnetic field is produced around it. When two or more coils are magnetically linked with each other, then an alternating current flowing through one coil causes an emf induced across the other linked coils. This phenomenon is known as mutual induction.

Now we will discuss Lenz’s law.

Lenz’s Law

Lenz’s  law of electromagnetic induction states that when an emf is induced according to Faraday’s law of electromagnetic induction, the polarity of that induced emf is such that it opposes the cause of its production.

Thus, Lenz’s law is given by

E = -N (dΦ/dt)   (volts)

The negative sign in above formula shows that the direction of the induced emf and the direction of change in magnetic fields have opposite signs.

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