Thermal expansion - Thermal Properties of Matter Video Lecture - Class 11

hello friends this video on thermal
properties of matter fact 5 is brought
to you by exam feel calm no more fuel
from exam please make sure that you have
watched all the visuals from part 1 2
but for before going ahead with part 5 I
would have talked about the basics of
heat temperature and units and scales
related to temperature we can start the
topic on thermal expansion
basically if thermal properties of
matter these are basically the
properties which we are mainly going to
do in this chapter so what can you think
about it knowing the name thermal
expansion thermal means something
related to heat expansion means
something which expands or something
which increases in its size right so
thermal expansion is nothing but the
phenomenon of increases in dimensions of
a body due to increase in its
temperature so as the links that is
thermal is heat or temperature expansion
is increase in size of water so increase
in the size of an object due to increase
in temperature for example if you heat a
particular object it starts increasing
in size so that is known as thermal
expansion that is the expansion is
taking place due to heat due to
application of heat now the next
question is what causes thermal
expansion and why is it that if you heat
an object it will expand what causes it
to expand when the think of a scenario
when I talk to an object any object in
this universe is nothing but matter
right no matter in term is made up of
one roots which in turn and ends up with
atoms right so what happens is when you
heat an object the molecules inside
that object they are set in random
motion what if you start moving here and
then they start vibrating now as a
result what happens is the molecules
tend to keep larger distance from each
other and you think of this scenario in
this way let us suppose as there is a
certain object which is made up of
molecules let us suppose initially the
molecules are arranged in this way now
you heat this substance and what happens
the molecules start moving randomly here
and here so here if you see even though
the number of molecules will remain the
same even now the number of molecules
will be the same but since they are
moving randomly here and there they are
not pleased
orderly one after the another so they
are not going to moving here and there
as a result they are keeping great and
average distance with each other as a
result when you see that entire object
as a whole it seems to you here if you
see this was your object but here if you
see this is your object so what do you
feel you feel as if the object expanded
the object is listed in size so very
simple answer is when heated particles
get random and thus usually maintain a
little average separation I hope it is
clear to you as it said when we heat the
substance it expands similarly if we
cool the substance it tends to contract
that is a substance generally tend to
decrease in size when it is cooled so
contraction of substances
who is referred to as negative thermal
expansion thermal contraction is
generally not used for this because when
people have this this thing in their
mind that if for expanding it is
expansion then for contracting the
contraction but in terms of physics
mostly we record it as thermal expansion
and negative thermal expansion when I
say negative thermal expansion I mean I
am talking about the scenario where a
substance is cooled and as a result it
is on writing so that is what negative
thermal expansion let us look at certain
examples of thermal expansion as I told
you
thermal expansion is all about increase
in size of an object when it is heated
that is when the temperature increases
the size of the object also increases
now let us look at thermal expansion in
case of solids most substances expand on
heating and contract on cooling however
there are exceptions and the most
important exceptions water we will
discuss about water in a separate slide
later let us consider solids first you
would have seen that while welding of
metal sparked by constructing some
furnitures or something made up of or
some machinery parts made up of metals
what happens is let us suppose you have
a small ring somewhat like this this is
a ring and in this ring you have to fill
in this circular metal plate now if you
see this you can very easily say that
this plate cannot fit inside this ring
because it is very small so how do we
fit it we heat this ring so that it
expands once it expands we just fit it
fit the plate inside the ring and after
some time it again cools down the
temperature cools down and it comes back
to its original size but by that time so
what what is the advantage of fitting it
industry.the
play gets very tightly fitted inside the
ring so that there is no chance of
coming it out now somewhat like this
similarly let us consider the case for
liquids you take some water in a beaker
clinks the thermometer inside the water
to read the temperature you will see
that once you feed the water the level
of the water increases but as the
temperature bleeding from the
thermometer increases the level of the
water also increases rattles water
expands on heating and there is
expansion with rising temperature
similarly in case of gases you would see
that if you place you please a bottle
with a balloon tightly fitted on it
small keep it over a frying pan and then
heat it what happens you will see that
as it is heated the balloon inflates now
this inflation of the balloon is because
of the heat because of this heat the
temperature increases because of which
the size of the balloon increases that
means even through gases gases also
expand when heated so we saw solids
expand when heated liquids expands when
heated as well as gases expand when
heated just have a review this is how
the ring is expanded similarly the
balloon inflates as it is heated right
now we'll go ahead and look at different
types of thermal expansion thank you
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