Factors affecting heating effect of Current - Electric Current & Circuits, Science, Class 7 Video Lecture

hello friends this video on electric
current and its effects part eight is
brought to you by exam feel calm no more
fear from exam first which determine the
heat produced by the currents how do we
know how much heat will be produced by
the current now the various factors
which determine the amount of heat are
material of the wild length of the wire
thickness of the wire so these are the
three important factors so when I say
material of the wire what do we mean so
let us look at the jewels law of heating
a law which was given by the famous
scientist Joule he said that the heat
produced by current is proportional to
the square of the current resistance of
the wire and the time for which the
current flows through the wire so this
is known as this relationship is known
as the joules law of heating so let us
try to understand this relation in more
detail what is I is nothing but the
current flowing through the wire so if
more current is flowing through the wire
more heat will be produced what is our I
is resistance of the wire that is of the
conductor through which current is
flowing and what is T it is the time for
which current flows through the wire
time of current flow right now now we
try to see how these are the factors
which are involved in this relation so
when you say resistance of the wire how
do we determine the resistance of the
wire so resistance of a wire is directly
proportional to the length of the wire
and it is inversely proportional to the
cross-sectional area of the wire so that
is how it is dependent on length of the
wine and thickness what do we mean by
thickness of a wire so this is somehow a
wire looks like right it is like a very
thin cylinder so basically
area so this area is known as the
cross-sectional area and this is known
as the length so you see resistance is
dependent on both length as well as
cross-sectional area so we can say that
heat is dependent on length of the wire
and thickness of the wire and wire on
material of the wire because here
resistance also depends on the
resistivity of the wire and resistivity
for different wires are different so it
depends the wire that on what material
the wire is made up of so in these
industries I am referring to wire so
many times wire is left can be referred
to the heating element of any appliance
so that heating element could be a wire
that heating element could be something
else as well but the how much heat will
be produced by a specific amount of
current is determined by the properties
of the heating element so now let us
look at some important applications of
heating effects of current so one such
important and useful applica application
is fuse what is a fuse have you ever
heard of fuse so you would have seen
that often people say there's some times
when there is a power cut they see that
you know the fuse went off and that is
why the power is gone so what do what is
that fuse so fuse basically is an
element which prevents excessive flow of
current through a circuit because if too
much current flows through a circuit
that can't destroy the circuit so it is
necessary to put a limitation in the
amount of current that can flow through
that circuit because excess time can
also spoil the other elements of the
circuit all right so this fuse is always
connected in series with the device so
that it can protect the device from
unwanted extra amount of current for
example think of your refrigerator if
too much of current starts flowing
through your refrigerator your
refrigerator will sometimes it will be
destroyed it will get spoiled so we have
to prevent that exist flow of current
through the circuit of your refrigerator
so for that we use a fuse which is
connected in series with the circuit of
the refrigerator and how different fuses
have different ratings like they can be
one happier two and pa3 amplify happy so
that depends on where they are do used
so here you can see the picture of a
fuse
now how fuse works on the principle of
heating effect of current now how it
prevents excessive flow of panic that is
more important to know now what happens
is this fuse is made up of a wire which
has considerably a lower melting point
so that when you would amount of current
passes as the amount of current
increases what will happen as current
would increase the amount of heat
produced will also increase as per jules
law of heating now since the middle of
which the fuses made up of that has a
considerably low melting point so as
soon as the heat reaches a certain value
it will melt so that means as soon as
that wire melts what happens the circuit
is broken now as soon as the circuit is
broken there is no flow of current so it
prevents any further flow of current so
now when a switch is rated one ampere it
allows up to one ampere of current to
flow through it whenever the current is
more than that it breaks due to
overheating and that's how it prevents
further flow of current through the
circuit now another important
application you have these these McD's
are substitute two switches they are
preferred over switches so what are
McD's you would have seen these kind of
structures in your home also so LCDs are
miniature circuit breakers why are they
called circuit breakers because even
they help to break the circuit in case
of excess current so whenever there is
excess current flow in low voltage
circuits they will help to prevent the
flow of current so what happens with
these circuit breakers is that when
overload condition or when excess of
current flows or other faulty condition
happens in the circuit it automatically
switches off the election
in seconds the entire circuit gets
switched off now how is it different
from fuse is that in fuse you have a
wire and the wire melts and breaks but
in this case nothing like that happens
as soon as the current gets overloaded
it gets heated above us beyond a certain
limit then the entire self it is
switched off so it is only about
switching on and off so there is no
breaking of wires or anything so that
means it is more reliable than fuse in
sensing the amount of current flow it
can sense it in a better way so fuse
might fail at certain situations but
McD's never fail so that is why it is
more commonly used than fuse one
advantage is that here there we have
Auto turn off during 40 condition so in
case you had ever observed this in your
houses so this switch which you see it
goes up and then again you can pull it
down so that's how it can be switched on
and off so that means it is very simple
to handle but in case of fuse once the
fuse wire is broken you cannot repair it
yourself you would need to call an
electrician and then he has to handle it
with care so it is a complex process so
this is easy to restore safe to handle
so restoring it is like let's say it
will switched off so how do you switch
on just pull it down that's all you have
to do safe to handle because you are not
handling with there is no direct contact
with wires etc so there are less there
are no chances of electric shock so that
means it is safer easy to identify the
faulty zone now when the MCB trips and
their faulty condition it trips only had
a particular position which helps to
identify the faulty zone easily now
McD's are arranged like this so in
whichever zone there is a problem only
that zone good trip the others would
remain still fine so that means it can
be easily determined where the fault is
so that means there are a couple of
advantages associated with McD's which
make them more popular than fuse thank
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