Eddy Current Disadvantage & Application - Electromagnetic Induction, Physics,

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let us look at the disadvantages of eddy
currents first so the very first
disadvantages it dissipates electrical
energy in the form of heat so this is a
big disadvantage of eddy currents
because as I mentioned you in the
previous slide what what was happening
when that metal plate is coming in the
magnetic field because of change in flux
that it is getting induced in the feet
now as more and more current keeps
getting inducing so the amount of
current in black metal plates increases
now when the amount of current increases
the heat dissipation also increases
because power which is dissipated in the
form of heat is equal to I square R that
means it varies with I square so if your
current is increasing your heat
dissipation is increasing as square of
current so you can imagine how fast your
power dissipation is increasing right so
because of this fact that eddy currents
get developed very quickly and it keeps
increasing with magnetic fields
therefore the dissipation of heat also
increases which is a very big decision
disadvantage because we due to this heat
overheating of metallic cores of
transformers electric motors and many
other such devices take place and
overheating of the core can spoil the
device right so we nobody will want that
the core should get overheated because
transformers electric motors or
generators they are all used for
practical purposes for our day-to-day
life right so and we use them and they
are very roughly used right so that it
is very obvious that if the core what is
the core made of the core is nothing but
it is some metal core which is again
wound with some metal metallic wire
right so because of that arrangement it
will get heated very quickly and
if it sometimes this overheating might
also melt some wires or it can destroy
the instrument on its own right so how
do we prevent this so there is a way by
which we prevent this overheating of
metallic cores so what do we do
generally very thin sheets of metal
metallic cores taken in the form of thin
metallic sheets they are taken in the
form of sheets and that is electrically
insulated by some insulating material
for example if this is your code you
insulate with your core with some
insulating material so now your heat
cannot get transferred to the wires or
the things surrounding it because there
is an insulating material around it so
this kind of course are known as
laminated course so generally the
insulating material which we use is
something like lacquer so because of
this laminated course you are in a way
reducing the eddy currents right so once
the eddy currents are reduced so your
heat dissipation is also reduced so
because of the use of these laminated
pours the eddy currents are reduced now
once you are able to reduce the eddy
currents your heat dissipation will also
reduce because current reduced metric
means that your I reduced I reduce means
this power which is dependent on I
square will also get greatly reduced
therefore the heat loss will be reduced
to a large extent right so this was the
negative part of eddy currents now there
are certain advantages of eddy currents
as well I mean there are certain places
where eddy currents play a very
important role and which is advantageous
to us for example when we talk about
electromagnetic breaks eddy currents
play so let us now see what is the role
that eddy currents play in
electromagnetic breaks when the talk of
electromagnetic breaks we are talking of
the fun the breaks which are used to
control the speed of fast-moving
electric trains which you would have
mostly seen a
right in those streams the arrangement
is such that on the tracks there are
excellent places big magnets are placed
near the track so with the help of those
magnets currents are induced on the
wheels of the Train so before that let
us try to understand what was the need
of having electromagnetic rates why is
why are these kind of rates advantages
so if you what do you get in your mind
when you think of brakes you remember of
the normal mechanical brakes or the
friction brakes right so friction brakes
are generally the cause I mean how do
they operate they operate by rubbing so
that involves wear and tear which turns
out to be little expensive because in
due course of time you need I mean you
need to maintain it because wear and
tear will happen but when you consider
the electromagnetic brakes it is like a
very cheap alternative to your friction
rings because it doesn't need any
maintenance at all you just need a
magnet which is to be placed near the
railway track so that the magnet can
produce a magnetic field and because of
that magnetic field it can induce a
current in a nearby circuit so that is
it so this electromagnetic induction
doesn't need any other apparatus
it doesn't need any other maintenance
there is no wear and tear involved at
all so therefore it is a very economical
alternative to friction brakes right so
what happens in this electromagnetic
brakes now we will see it in detail let
us suppose that we have placed a very
big magnet somewhere nearby the track on
which the train will be moving so now
what happens as let us imagine this for
now you consider that this wheel is the
wheel of the fast-moving electric train
okay so we imagine that the outer rim of
the wheel is coated with copper so
copper is mounted on the wheels
so what will happen as this V comes near
by the magnet as soon as it comes near
the magnet what will happen it will
the magnetic field produced by the
magnet there because of which there will
be a change in flux as you can see here
due to the motion of this wheel there
will be a change in flux which it will
experience so I mean Rios current will
be reduced so current will get induced
here now the direction of the induced
current will be given by lens law so
what does lens loss is it says that the
induced current will try to oppose the
cause which produced it so what is the
cause that produced it the movement of
the wheel towards this so the wheel was
moving towards this direction right so
the movement of the wheel towards this
direction resulted in induced current so
the induced current will be in such a
direction that it should push the wheel
back that means it will the induced
current will give rise to a repulsive
field here so there will be a repulsive
induced field here getting me now what
happens because of this repulsive field
the train will get little slowed down it
will slow down and as it moves further
and it reaches the other end of the
magnet what happens again here induced
current will be produced but this time
the direction of the current will be
opposite so it will give rise to an
attractive field here so as a result the
tree the wheel was moving this side
there was a repulsive field here so that
is it's like this that is why it got
little slowed down as it moved towards
the other end of the magnet or as the
front part of the train proceeded the
back part of the train carried forward
so as it reached the other end now it
experiences an attractive feature that
is now it is pushed back again so as a
result the Train gradually slows down
and finally it is pulled back and it
comes to rest now when you think of it
it is I mean it is really difficult to
imagine that all this happens within
fraction of seconds I mean this brakes
are applied almost immediately but the
concept behind this lies in this but
things happen so fast that you just see
the electromagnetic brakes being applied
almost at this
of a moment so in this case the kinetic
energy lost by the Train is the heat
gained by the copper now what is
happening here because of this magnetic
field the induced current is where the
induced current is flowing through the
copper right so that kinetic energy lost
by train is nothing but the heat gained
by copper so that is how it it it obeys
the law of conservation of energy so if
you now if you see the importance of
Lenz law if you understand Lenz law very
clearly then it is very easy to
understand all the practical phenomenon
which happen around us now so you can
see it you can try it for yourself that
if you find out the direction of current
at this point and the direction of
current at this point they will be
opposite in this case the current will
try to oppose the motion of the wheel
which was towards this direction so the
current will want it to move along this
direction similarly when it reaches here
now what induces the current the motion
of the wheel towards this direction
therefore the current wants the wheel to
move towards this direction so every
time the current wants to push it back
so as a result that train finally stops
so another good application of eddy
currents is the electromagnetic damping
so now even in this case that is in case
of electromagnetic brakes we saw that
because of the production of eddy
currents the motion was opposed the eddy
currents were always trying to oppose
the motion of the train and finally the
train stopped right so either way the
this property of eddy currents that it
opposed relative motion it innovators of
help to us right the disadvantage also
turns out to be advantageous in some way
now let us look at another important
application which is electromagnetic
damping this is something related to
what we discussed
our previous example where I allowed a
metallic plate to swing between two pole
theses of a magnet that means in
presence of magnetic fields if you allow
a metal plate to oscillate what will
happen you will see damping that is the
amplitude will gradually reduce and
eventually it will come to rest so this
electro magnetic damping phenomenon is
extremely useful in galvanometers why
because what happens in galvanometers in
Kelvin the nano meters are the
instruments which help us to detect
current right so when current passes
through a galvanometer there is a needle
inside it which is that needle is
nothing but a small metal plate which is
allowed to oscillate so that small metal
plate starts oscillating and after some
time it comes to rest so when it comes
to rest that is when we determine the
magnitude of the current given by the
galvanometer so by using this phenomenon
of electromagnetic damping the metal
plate which oscillates it can come to
rest quickly because if that if there is
no electromagnetic damping the metal
plate which is oscillating inside the
galvanometer it will keep oscillating
for an indefinite period of time so I
mean it will I mean you it the time will
not come when when it will be static and
you will be able able to read the
current right so for we have an ammeter
it is very much important that there is
electromagnetic damping so that the
oscillating metal piece can come to rest
and we are able to detect the van so
here also the same concept is there that
is when the metal the metal plate
oscillates in magnetic field while
entering the magnetic field there is a
current induced similarly by leaving the
magnetic field there is a current
induced but the current induced while
entering and the current induced by
leaving they are in opposite directions
so these eddy currents so I mean it
keeps happening over and again right so
it enters leaves and those leaves enters
leaves so so many times the currents
keep inducing so these eddy currents
oppose the relative motion as an aside
electromagnetic dam
being occurs so this phenomenon that
eddy currents oppose relative motion has
many good uses where we can really find
it where it really turns out to be
advantageous however many people see
that 80 parents or something which which
are undesirable but it is not always
undesirable we are true that it has got
certain very big disadvantages like the
huge amount of heat loss is a very big
disadvantage but still the positive part
of it can also be looked upon because it
it gives us or it finds uses in our
day-to-day life so I hope the concept of
eddy current is now clear to you thank
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