We have studied about Hans Christian
Řrsted discovery. The discovery that he
made that a current-carrying conductor
was responsible for creating a magnetic
field around it.
Now Michael Faraday was a scientist, who
discovered the opposite that with the
help of a magnetic field we can produce
electricity. Now Michael Faraday had
simple beginnings.
He was the son of a blacksmith and he
worked as a bookbinder. Now Michael
Faraday in his youth not only bound the
books but he also read them. Now while
reading them he came to know about
Christian Řrsted discovery and he got
to thinking that if it is possible to
create a magnetic field with the help of
electricity,
it must also be possible to do the
reverse and indeed it was
and the breakthrough was made by him and it is
because of Michael Faraday that today
we are able to enjoy uninterrupted power supply even during load-sheddings and
power cuts and you can enjoy the fan the
light and even your television show
even when there is load-sheddings or power cuts.
So now let us take a look at a video
which demonstrates the experiment that
Faraday had conducted. Now this was the
experiment conducted by Faraday in
order to demonstrate the fact that with
the help of magnetic field it is able to
generate electricity. Now over here, a bar
magnet has been taken along with a coil
the ends of which are connected to a
galvanometer. So you will notice that as
the magnet is brought near the coil,
the galvanometer shows a slight deflection.
When the magnet is taken away from the
coil, the galvanometer shows a slight
deflection in the opposite direction but
you will also notice that if the magnet
is kept stationary then there is no
deflection in the galvanometer. So let us
find out what exactly is going on.
We know that a magnet in this case a bar
magnet as magnetic field all around it.
This magnetic field is represented by
the magnetic field lines from north to
south. So firstly, when we find that the
magnet is at rest we will see that the
galvanometer needle shows no deflection,
why, because when the magnet is at rest
the number of magnetic field lines due
to the magnet passing through the coil
remains constant or in other words we
can say that when the magnet is
at rest, the number of field lines linked
with this particular coil that we have
considered is constant and as a result
there is no deflection in the galvanometer
needle. It remains stationary or fixed
at the zero mark. Now notice what happens
when the magnet is moved. As you can see
once the magnet is moved into the coil,
the number of magnetic field lines
through the coil increases and when it
is moved away from the coil, the number
of magnetic field lines through the coil
decreases. So we can say due to movement
of the magnet, the number of magnetic
field lines either increases or
decreases through the coil.
So as you see, the total number of
magnetic field lines is changing and
this has a particular name. The total
number of magnetic field lines due to
the magnet passing through the given
coil is known as the magnetic flux
linked with the coil. So when we find
that the number of field lines is increasing, it
means that the magnetic flux linked with
the coil is increasing and when the
magnetic field lines are decreasing, it
is the magnetic flux linked with the
coil that is decreasing.
So the change in magnetic flux is what
is resulting in the deflection of the
galvanometer. We found that when magnetic
flux remains constant,
there was no deflection in the needle,
However, whenever there was a change in
magnetic flux a deflection in the
galvanometer was present.
This deflection in the galvanometer implies
that a current is present in the circuit.
How can we say that because we know that
galvanometer is an instrument which
measures current and also denotes the
direction in which current flows. So the
moment there is a deflection in the
galvanometer, we cannot only say that
there is a current that is present in
the circuit we can also say in which
direction that current is flowing.
Now we have studied that whenever
current has to flow there should be the
presence of a certain electrical
potential difference. Now this electrical
potential difference should be applied
at two ends of the circuit so only when
there is an electrical potential
difference current will flow. Now this
electrical potential difference is also
known as EMF or the electromotive force.
So thus we can say that for current to
flow there should be the presence of EMF
or an electromotive force. Now what did
we find? We found that whenever the
magnet was been moved there is a
deflection in galvanometer which means
that there is the presence of a current.
So if there is a presence of current, we
can say that there is an EMF and this
EMF has been induced due to the movement
of the magnet or the change in magnetic
flux.
So because there is a change in magnetic
flux, it results in the production of an
induced EMF. So whether it be that the
magnetic flux is increasing or
decreasing, it means there is a change
and thus there is the production of
induced EMF. So this phenomenon is known
as electromagnetic induction.
Electromagnetic induction is nothing but
reproduction of an induced EMF due to
change in magnetic flux. So how do we
define electromagnetic induction?
Electromagnetic induction is defined as
the phenomenon in which an EMF is induced
in the coil due to change in magnetic
flux linked with the coil. Now again
there are a few things to be kept in
mind. The first and foremost thing is
that an EMF is induced only when there
is a change in magnetic flux linked with
the coil. It doesn't matter what change
in magnetic flux is taking place outside
the coil only when there is a change of
magnetic flux linked with the coil or
passing through the coil only then will
an EMF be induced. As a result, induced
current is produced that flows in the
closed circuit and the direction of it
as we saw could be found out with the
help of a galvanometer.
So now let us look at a simulation which
will demonstrate the experiment that
Faraday had conducted. So over here, i
have taken a bar magnet with its north pole
on the right inside and south pole on
the left-hand side and i have also taken
a coil. Now as you can see the ends of
this coil are connected across a device
that will indicate the EMF that is being
produced. It will also show us in which
direction the current through the coil
is flowing. So let's say i take this coil
and i move it inwards or towards the
coil. As you can see there was a slight
deflection to be negative side of this
particular device. So this means that
current is flowing in this direction. Now
notice what happens when i drag it out?
There was a deflection in the opposite
direction. Now as you can see when i'm
keeping this magnet stationary or at
rest, there is no deflection taking place
but the moment and moving it inwards,
there is a certain deflection. The moment
i move it outwards again there is a
deflection but in the opposite direction.
Now as you can see this direction gives
us the direction in which current flows
and this is purely because there is the
change in magnetic flux linked with this
particular coil . Now in this animation
you will find that when the magnet is
being moved towards the coil slowly,
there is a certain deflection in
the galvanometer, however, if it is being
moved in and out towards the coil and
away from the coil faster than the
deflection in the galvanometer is more than
the previous case. So what does this
imply? This implies that if we move the
magnet fast inwards and outwards from
the coil then the galvanometer
deflection will be more and then the
movement is slow and the galvanometer
deflection will be less. This leads us to
a very important conclusion.
That conclusion is that if the rate of
change of magnetic flux is more or in
other words if their rate at which the
magnetic field lines linked with the
coil is more or increased that means the
induced EMF will also increase.
Conversely, if the rate of change of
magnetic flux is decreased or is less
than the induced EMF will also decrease
as we found out in the previous
animation. So this implies that the
induced EMF is directly proportional to
the rate of change of magnetic flux or
in other words if we increase the rate
of change of magnetic flux or if it is
more, it will imply that the induced EMF
also increases. Similarly if we decrease
the rate of change of magnetic flux or
if it is less then it will imply that the
induced EMF also decreases or is less.
So Faraday after studying about
electromagnetic induction postulated
these laws. These laws are known as
Faraday's laws of electromagnetic
induction and they state whenever there
is a change in the magnetic flux linked
with the coil, an EMF is induced. The
induced EMF last as long as there is a
change in magnetic flux linked with the
coil. So only as long as there is a
change in magnetic flux, the induced EMF
for last and the second law states that
the magnitude of induced EMF is directly
proportional to the rate of change of
magnetic flux linked with the coil.
Greater the rate of change of magnetic
flux more will be the induced EMF less the
change of the rate of change of magnetic
flux less will be the EMF.
Now let's take a look at the video a
previously showed you and notice one
important aspect. In this video, you will
find that the same experiment that
Faraday had conducted is being repeated.
Now notice that when the bar magnet is
being moved in the galvanometer needle
is deflecting towards one side and when
the magnet is being moved out the
galvanometer needle is moving to the
opposite side as i showed you in the
simulation as well. Now you might be
wondering that in order to find out the
direction in which current is flowing, is
it always necessary to use such an
experimental setup? Isn't there any
alternative way in which we can find out
the direction in which current is
flowing? The answer is, yes we can.
That rule was given by Fleming. Now we
Have earlier studied about Fleming’s
left-hand rule. In this case, the
direction of current induced can be
found out with the help of Fleming’s
right hand rule. So what does Fleming’s
right hand rule state? It states that if
you stretch out your forefinger in the
direction of the magnetic field and if
you stretch out your thumb in the
direction of the force,
then if you stretch out your middle
finger perpendicular to both, the thumb as
well as the forefinger, that will give
you the direction of current. So if we
consider the image on the board you will
find that the magnetic field is in this
direction the force is being applied in
the upward direction. So obviously if I
stretch out my middle finger
perpendicular to both the forefinger as
well as the thumb then the direction in
which the middle finger is pointing will
give me the direction of current. So in
this case, the direction of current is
this.
So as you can see if we use Fleming's
right hand rule instead of going through
such an elaborate experimental setup we
can also determine the direction of
induced current
