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
electromagnetic
induction now if we focus on the coil
example when there is relative motion
between the coil and the magnet the
magnetic field lines cutting through the
coil are changing the magnetic field
lines linked with the coil is called
magnetic flux it is this changing
magnetic flux linked with the coil that
induces a current in the coil how can we
find the direction of the current
induced in the coil earlier we had
learned about Fleming's right hand rule
to find the direction of the induced
current for a straight wire to find the
direction of the current in the coil we
can use a law called lenses law
lens's law states that the direction of
the induced current is such that it
opposes the cause which produces it
let's apply lens's law to our
example let's say the North Pole of the
bar magnet is moving towards the coil as
shown here the induced current will flow
in such a direction that there is a
North Pole on the end two of the coil
and a South Pole on the end one of the coil
coil
now the coil can repel the magnet
because according to lens's law the
induced current should flow in such a
direction that it opposes the cause that
produces it so it's opposing the motion
of the magnet here and remember the
clock phas rule to produce a North Pole
on N2 of the coil what should be the
direction of the induced current if
you're looking from
N2 that's right the current will flow in
the anticlockwise direction and that's
how a North Pole is produced at N2 and a
South Pole at end one so lens's law
helps to find the direction of the
induced current in the
coil now when the magnet is moved away
from the coil the current will flow in
the clockwise Direction and it will
produce a South Pole at end2 and a North
Pole at end one now let's see how the
magnitude of the current induced in the
coil can be
increased one way to increase the
current is to increase the area of
cross-section of the coil and increase
the number of turns in the coil another
way is to increase the strength of the
magnet you can also increase the speed
of the relative motion between the coil
and the
magnet this will increase the induced
current now let's place these different
ways to increase the magnitude of the
induced current in the coil on our
concept board now let's look at another
interesting case of electromagnetic
induction where there's no magnet we
just have two coils placed side by side
as shown here coil a is connected to a
battery and a switch and coil B is
connected to a
galvanometer what do you think will
happen when you press the switch on coil
a current will pass through the coil a
but something interesting is observed on
the galvanometer in coil B when the
switch is pressed the galvanometer shows
deflection for a short time and quickly
returns back to the zero position this
means that a current has been induced in coil
coil
B now when the switch is turned off in
coil a there is again a deflection in
the galvanometer but now in the opposite
direction the galvanometer deflection is
there for a short time and the pointer
quickly returns back to the zero
position now what do you think will
happen if you keep playing with the
switch and keep on switching it on and off
off
continuously that's right the
galvanometer pointer keeps on moving on
both the sides and this shows that an
alternating current is induced in coil
B but how is electromagnetic induction
happening without a magnet here let's
take a closer
look initially the switch in coil a is
in the off position when we switch on
the current in coil a it becomes an
electromagnet coil a produces a magnetic
field around it the magnetic field lines
go and cut through coil B it's like
pushing a magnet into coil B B so a
current is induced in coil B and there
is a deflection in the
galvanometer when the current in coil a
becomes steady the magnetic field lines
cutting through coil B also become
steady now there is no changing magnetic
field so the current in coil B becomes
zero when we switch off the current in
coil a the magnetic field lines will
disappear this is like pulling a magnet
out of coil B so a current will be
induced in coil B but in the opposite
direction the galvanometer deflects in
the opposite direction a changing
magnetic field induces a current in coil
B this happens when the current in coil
a is switched on and when it is Switched
Off if we keep switching the current on
and off continuously in coil a the
magnetic field will keep on changing so
a current will continuously be induced
in coil B the current will be
alternating in nature so an alternating
current will be induced in coil B I hope
the concept of electromagnetic induction
is super clear to you now do you know
where this principle is practically
used that's right in an electric
generator there is relative motion
between the coil and the magnet in the
generator this induces current in the
coil and that's how electricity is is
produced by a
generator and that's how we get
electricity in our homes and offices
it's being produced by a generator
located in a par station far away from
the city and to revise the concepts just
go to my website Manoa
academy.com to make it easy I'll put the
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