The core theme is electromagnetic induction, the phenomenon where a changing magnetic field can produce an electric current, and the principles governing this process, including Fleming's right-hand rule and Lenz's Law.
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hi friends as we discussed in an earlier
video a current carrying wire produces a
magnetic field around it this is called
magnetic effect of electric current or
electromagnetism so electricity produces
magnetism but is the reverse also true
can magnetism produce electricity the
answer is yes this phenomena is known as
electromagnetic induction and that
that's going to be the topic of this
video we are also going to look at
Fleming's right hand rule and lens's law
I'm going to make the concepts really
easy for you the production of
electricity from magnetism is called electromagnetic
electromagnetic
induction and the electric current that
is produced is called induced current
electromagnetic induction was discovered
about 200 years back in
1831 it was discovered by British
scientist Michael Faraday and an
American scientist Joseph Henry
independently let's understand
electromagnetic induction with a simple
experiment for the experiment we'll use
a horseshoe magnet a straight wire is
held between the North and South Poles
of the horseshoe
magnet the two ends of the wire are
connected to an instrument called a
galvanometer you might have seen a
galvanometer in your lab
this do you know what a galvanometer is
used for that's right to detect the
presence and direction of electric
current when there is no current the
galvanometer needle points to the zero
Mark now I'm going to pass electric
current through this
galvanometer as you can see there's
deflection in the needle it deflects to
the right side of zero
indicating the flow of current to
reverse the direction of current in the
galvanometer I'm going to switch the red
and black wires on the galvanometer now
when I switch the wires and turn on the
voltage Supply can you see that the
galvanometer needle deflects in the
opposite direction to the left side of
zero because the direction of current is
opposite now when the wire is stationary
that is the wire is held in the magnetic
field without moving it the galvanometer
does not show any
deflection so when the wire is
stationary there is no electric current
in the
wire now when the wire is moved upwards
rapidly there is a deflection in the
galvanometer this indicates that
electric current is produced in the wire
this is called induced
current electric current can be produced
only when there is a potential
difference so a potential difference
difference or voltage has been induced
across the ends of the wire this induced
voltage is called electromotive force or
EMF in
short note that the galvanometer
deflection lasts for a very short time
the EMF and electric current are
produced in the wire as long as there is
motion of the wire when the motion stops
there is no EMF and hence no electric
current to keep things simple in this
video we'll not use the term
electromotive Force EMF a lot we will
just use the term induced current now if
we move the wire downwards rapidly
between the poles of the horseshoe
magnet again there is a deflection in
the galvanometer but the deflection is
now in the opposite
direction so electric current is
produced in the wire but the direction
of the electric current is opposite
again the deflection in the galvanometer
is for a very short time and lasts as
long as there is motion in The Wire so
this experiment shows that when a wire
is in motion in a magnetic field
electric current is produced in the wire
what do you think will happen if you
move the wire up and down continuously
in the magnetic
field that's right a continuous current
will be produced in The Wire when the
wires moved up the current flows in One
Direction and when the wires moved down
the current flows in the opposite
direction the direction of electric
current will keep changing continuously
as the wires moved up and down do you
know what is this current known
as that's right alternating current or
AC in short because the direction of the
current keeps on alternating changing
let's understand why electric current is
produced in a wire when it is moved in a
magnetic field when the wire is moved in
a magnetic field the free electrons
present in the wire experience a force
this Force makes the free electrons move
in the wire in a certain
direction and what is the movement or
flow of electrons known as that's right
electric current so when a wire is moved
in a magnetic field an electric current
is produced in the wire because the free
electrons experience a force and that's
why they flow in The Wire electric
current is being produced so we can say
that electrical energy is being
generated the output here is electrical
energy but let me ask you where is this
energy coming from what form of energy
is being converted to electrical energy
that's right mechanical energy it's the
mechanical energy used to move the wire
that is being converted to electrical
energy as we have discussed when a wire
is moved in a magnetic field electric
current is produced in the wire so when
there's motion of the wire in the
magnetic field current is
produced this is called electromagnetic
induction now let's see how we can
predict the direction of the induced
current in the wire we use our example
of a straight wire in Motion in a
magnetic field to find the direction of
the current in the wire we need to use
Fleming's right hand rule remember we
had learned Fleming's left hand rule in
an earlier video to find the direction
of force on a current carrying wire
placed in a magnetic field and for
electromagnetic induction we need to use
Fleming's right hand rule for Fleming's
right hand rule hold your right hand
like this with the four finger Center
finger and the thumb at right angles 90°
angles to each
other the four finger represents the
direction of the magnetic field it's
easy to remember F for four finger f for
field the thumb represents the direction of
of
motion and the center finger represents
the direction of the IND indued current
you can remember it as C for Center
finger C for current let's see how we
can use Fleming's right hand rule to
find the direction of the induced
current when a wire is in motion in a
magnetic field like this the trick is to
consider each thing one by one let's
start with the magnetic field so what is
the direction of the magnetic field here
that's right the magnetic field is from
the North Pole to the South
Pole the four finger represents the
magnetic field so hold your forefinger
like this along the direction of the
magnetic field next let's look at the
direction of motion of the wire so
keeping the forefinger aligned along the
magnetic field now align your thumb
along the direction of motion of the
wire since the wire is moving upwards
the thumb is pointing up
upwards the center finger will
automatically give you the direction of
the current in the wire as you can see
the direction of the induced current is
outwards along the wire one important
thing to note is just like Fleming's
left hand rule Fleming's right hand rule
also gives the conventional direction of
the induced current not the direction of
flow of
electrons now what will be the direction
of induced current if the wire is moving
moved downwards here again let's use
Fleming's right hand rule the forefinger
points in the direction of the magnetic
field since the wire is moving downwards
the thumb which represents motion will Point
Point
downwards the center finger will
automatically give us the direction of
the induced current as you can see the
direction of the induced current is
inwards along the wire so out of these
three things magnetic field motion and
induced current if the direction of two
things are given to us we can use
Fleming's right hand rule to easily find
the direction of the third thing but
just remember to keep the three fingers
at 90° angle right angle to each other
you may need to rotate your hand at the
wrist in order to align with the
question that is given to you Fleming's
right hand rule may seem a bit difficult
at first but with practice I'm sure
you'll find it really easy let's go
ahead and put Fleming's right hand rule
on our concept board we discussed the
concept of electromagnetic induction
using a straight wire that is in motion
between the poles of a horseshoe magnet
now let's look at the experiment where
the wire is in the shape of a coil and a
bar magnet is used the two ends of the
coil are connected to a
galvanometer now let's take the bar
magnet and bring it near the
coil when we don't move the bar magnet
that is the magnet is held stationary
then there is no deflection in the
galvanometer this means that there is no
current in the
coil now when the bar magnet is moved
quickly into the coil a deflection in
the galvanometer is observed this
indicates there is current flowing in
the coil but when the magnet stops
moving the galvanometer reading shows
zero indicating there is no current
flowing in the coil now when the bar
magnet is moved quickly out of the coil
what do you think will happen that's
right the induced current in the coil
flows in the opposite direction the
galvanometer shows deflection in the
opposite direction now if the magnet is
continuously moved into and out of the
coil a continuous current is induced in
the coil the direction of the current
keeps changing alternating so an
alternating current is produced in the
coil due to electromagnetic induction in
the first example we saw that the magnet
was fixed and the wire was in motion and
a current was induced in the wire in
this example we saw that the wire a coil
is fixed and the magnet is in motion
again a current is induced in The Wire
so you need relative motion between the
wire and the magnet to induce a current
in the wire this is the principle of electromagnetic
