Faraday’s Laws of Electromagnetic
Induction: First & Second Law
What is Faraday’s Law
Faraday’s law of electromagnetic
induction (referred to as Faraday’s law) is
a basic law of electromagnetism
predicting how a magnetic field will
interact with an electric circuit to produce
an electromotive force (EMF). This
phenomenon is known as electromagnetic
induction.
Faraday’s law states that a current will be
induced in a conductor which is exposed
to a changing magnetic field. Lenz’s law
of electromagnetic induction states that
the direction of this induced current will
be such that the magnetic field created by
the induced current opposes the initial
changing magnetic field which produced
it. The direction of this current flow can be
determined using Fleming’s right-hand
rule.
Faraday’s law of induction explains the
working principle of transformers,
motors, generators, and inductors. The
law is named after Michael Faraday, who
performed an experiment with a magnet
and a coil. During Faraday’s experiment,
he discovered how EMF is induced in a
coil when the flux passing through the
coil changes.
Faraday’s Experiment
In this experiment, Faraday takes a
magnet and a coil and connects a
galvanometer across the coil. At starting,
the magnet is at rest, so there is no
deflection in the galvanometer i.e the
needle of the galvanometer is at the center
or zero position. When the magnet is
moved towards the coil, the needle of the
galvanometer deflects in one direction.
When the magnet is held stationary at that
position, the needle of galvanometer
returns to zero position. Now when the
magnet moves away from the coil, there is
some deflection in the needle but opposite
direction, and again when the magnet
becomes stationary, at that point respect
to the coil, the needle of the galvanometer
returns to the zero position. Similarly, if
the magnet is held stationary and the coil
moves away, and towards the magnet, the
galvanometer similarly shows deflection.
It is also seen that the faster the change in
the magnetic field, the greater will be the
induced EMF or voltage in the coil.
Deflection in
Position of magnet
galvanometer
No deflection in the
Magnet at rest
galvanometer
Deflection in
Magnet moves towards
galvanometer in one
the coil
direction
Magnet is held stationary
No deflection in the
at same position (near the
galvanometer
coil)
Deflection in
Magnet moves away
galvanometer but in the
from the coil
opposite direction
Magnet is held stationary
No deflection in the
at the same position
galvanometer
(away from the coil)
Conclusion: From this experiment,
Faraday concluded that whenever there is
relative motion between a conductor and
a magnetic field, the flux linkage with a
coil changes and this change in flux
induces a voltage across a coil.
Michael Faraday formulated two laws on
the basis of the above experiments. These
laws are called Faraday’s laws of
electromagnetic induction.
Faraday’s First Law
Any change in the magnetic field of a coil
of wire will cause an emf to be induced in
the coil. This emf induced is called
induced emf and if the conductor circuit is
closed, the current will also circulate
through the circuit and this current is
called induced current.
Method to change the magnetic field:
1.By moving a magnet towards or away
from the coil
2.By moving the coil into or out of the
magnetic field
3.By changing the area of a coil placed in
the magnetic field
4.By rotating the coil relative to the
magnet
Faraday’s Second Law
It states that the magnitude of emf
induced in the coil is equal to the rate of
change of flux that linkages with the coil.
The flux linkage of the coil is the product
of the number of turns in the coil and flux
associated with the coil.
Faraday Law Formula
Consider, a magnet is approaching
towards a coil. Here we consider two
instants at time T1 and time T2.
Flux linkage with the coil at time,
Flux linkage with the coil at time,
Change in flux linkage,
Let this change in flux linkage be,
So, the Change in flux linkage
Now the rate of change of flux linkage
Take derivative on right-hand side we
will get
The rate of change of flux linkage
But according to Faraday’s law of
electromagnetic induction, the rate of
change of flux linkage is equal to induced
emf.
Considering Lenz’s Law.
Where:
Flux Φ in Wb = B.A
B = magnetic field strength
A = area of the coil
How To Increase EMF Induced in a Coil
By increasing the number of turns in
the coil i.e N, from the formulae
derived above it is easily seen that if
the number of turns in a coil is
increased, the induced emf also gets
increased.
By increasing magnetic field
strength i.e B surrounding the coil-
Mathematically, if magnetic field
increases, flux increases and if flux
increases emf induced will also get
increased. Theoretically, if the coil is
passed through a stronger magnetic
field, there will be more lines of force
for the coil to cut and hence there will
be more emf induced.
By increasing the speed of the relative
motion between the coil and the
magnet – If the relative speed between
the coil and magnet is increased from
its previous value, the coil will cut the
lines of flux at a faster rate, so more
induced emf would be produced.
Applications of Faraday’s Law
Faraday law is one of the most basic and
important laws of electromagnetism. This
law finds its application in most of the
electrical machines, industries, and the
medical field, etc.
Power transformers function based on
Faraday’s law
The basic working principle of the
electrical generator is Faraday’s law
of mutual induction.
The Induction cooker is the fastest way
of cooking. It also works on the
principle of mutual induction. When
current flows through the coil of
copper wire placed below a cooking
container, it produces a changing
magnetic field. This alternating or
changing magnetic field induces an
emf and hence the current in the
conductive container, and we know
that the flow of current always
produces heat in it.
Electromagnetic Flow Meter is used to
measure the velocity of certain fluids.
When a magnetic field is applied to an
electrically insulated pipe in which
conducting fluids are flowing, then
according to Faraday’s law, an
electromotive force is induced in it.
This induced emf is proportional to
the velocity of fluid flowing.
Form bases of Electromagnetic theory,
Faraday’s idea of lines of force is used
in well known Maxwell’s equations.
According to Faraday’s law, change in
magnetic field gives rise to change
in electric field and the converse of this
is used in Maxwell’s equations.
It is also used in musical instruments
like an electric guitar, electric violin,
etc.
