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:-
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)
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.
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