Thursday, November 5, 2015

Faraday's law of electromagnetic Induction

Faraday’s law of electromagnetic induction explains about working principle of following:-
(i)                   Induction Motors

(ii)                  Generators
(iii)                 Transformers
(iv)                 Inductors
This law was given by Michael Farday.

This law provides relationship between current and magnetic field.



There are two Faraday laws of Electromagnetic Induction as stated below:-
Faraday's First Law of electromagnetic Induction
According to this law whenever there is change in the magnetic field of a coil there will an emf to be induced in the coil. This induced emf is called as induced emf.
If circuit of conductor is closed then induced current will also circulate through the circuit.

There are following Methods to change magnetic field

(i)                   Magnetic field can be changed by Moving magnet away or towards the coil
(ii)                  Magnetic field can be changed by moving coil into or out of magnetic field.
(iii)                 Magnetic field can be changed by changing area of magnetic field in which coil is placed.

(iv)                Magnetic field can be changed by rotating coil relative to magnet.
Faraday's Second Law of electromagnetic Induction
According to this law the magnitude of emf induced in the coil is equal to the rate of change of flux that linkages with the coil.

Flux linkage of the coil is the product of number of turns in the coil and flux associated with the coil.

How Faraday law of electromagnetic Induction works:-
Let’s take a Galvanometer connected through a coil as shown below:-

Faraday's law of electromagnetic Induction

 Now when a Magnet is taken close to this coil, galvanometer needle get deflected from its center position in one direction. Now if galvanometer is taken back to it’s original position then needle will get deflected towards it’s original position.
Similarly if we take galvanometer in opposite direction then Galvanometer needle will move in opposite direction indicating a change in polarity. Then by moving the magnet back and forth towards the coil the needle of the galvanometer will deflect left or right, positive or negative, relative to the directional motion of the magnet.




Now let’s consider magnet approaching towards a coil. Now consider instants Ta and Tb:-
Now Flux linkage with the coil at time, Ta = NΦa Wb
Flux linkage with the coil at time, Tb = NΦb wb
So Change in flux linkages will be = N(Φb – Φa)
Now change in flux linkage will be, Φ = Φb – Φa
So, the Change in total flux linkages will be  = NΦ
Rate of change of flux linkage = NΦ / t
Since flux is changed at two instants so by taking derivative on right side of equation we get rate of change of flux linkage = NdΦ/dt
According to Faraday’s law of electromagnetic induction rate of change of flux linkage is equal to emf.
So get
E= NdΦ/dt ---- (i)
Where flux Φ in Weber = B.A ----- (ii)
Where, B = magnetic field strength
A = area of the coil

Methods of increasing Induced EMF in a Coil
From equation (i) and (ii) we see that Induced emf depends upon Number if turns of coil(N), Magnetic field strength, area of coil. Now to increase Induced EMF following all above three parameters should be increased or decreased as per description below:-

(a)          By increasing magnetic field strength, which in represented by B in formula. Now we see that by increasing magnetic field strength flux increases and this will leads to increase in induced emf.
(b)          By increasing No. of turns of coil induced EMF get increased as induced EMF is directly proportional to Number of turns of coil.
(c)          By increasing area of coil flux linkage with coil get increased so induced EMF get increased.
(d)          There is fourth method of increasing the induced EMF i.e. by increasing speed of relative motion between coil and the magnet, As increase in relative speed will cause to cut more lines of flux at faster rate and EMF produced get increased.

Faraday’s laws applications:-
Faraday law of electromagnetic induction is applicable on most of electrical systems and Transformers, Induction Motors, generators, Induction coils all works on Faraday’s law of electromagnetic induction.