L7 : Mercury In Thermometer - Heat, Science, Class 7 Video Lecture

hello friends this video on heat pack 7
is brought to you by exam floor comm no
more fear from exam now we looked at
both clinical as well as laboratory
thermometers everywhere we see that now
it is always a Chosen mercury which is
used as the liquid inside the
thermometer now what is so special in
mercury that it is in demand for making
thermometers firstly it is liquid at
room temperature and we want a liquid so
that the liquid can actually move
through the tube so you see this is the
thermometer now along the length of the
thermometer had it been a solid it would
have not have that much of motion that
mobility would have not been there but
since it is a fluid so it can like flow
from one place to another so since it is
a liquid so that is a good thing
secondly it has high coefficient of
expansion now what do we mean by high
coefficient of thermal expansion
expansion means anything which is
expanding anything which is increasing
in its volume thermal expansion means
anything which is expanding due to heat
so mercury has high coefficient of
expansion means that even if it is
heated very slightly mercury expands
noticeably so even if you apply a little
bit of heat so it will start expanding
so and that expansion will be noticeable
so now if you start using a liquid which
has low coefficient of expansion in that
case what will happen the that liquid
will not be able to give you very small
temperature so because when you have
like small temperatures that liquid will
not expand so the liquid does not expand
you really don't see anything
or you really do not your thermometer
does not read anything so this is one of
the most important reasons why mercury
is used in thermometers besides this the
liquid this it has a property that it
does not stick to the walls of the
thermometer now if it starts sticking to
the walls of the thermo
there is a case again it will not be
able to flow along the length of the
tube so that is also another important
thing it has a shiny appearance which
makes it easier to read the thermometer
because that shiny line can be seen
distinctly it has a low melting point
somewhere around -38 degree Celsius and
a very high boiling point so therefore
the chances of this mercury being melted
or getting boiled is very less because
normally now if some an object has very
high melting point or very low boiling
point and what happens is maybe even at
room temperature it might start boiling
not as soon as you expose it to some hot
substances at Mike's add boiling so all
those lists are not there because it has
a low melting point so it will start
melting only at a very very low
temperature similarly it will start
boiling only at a very high temperature
so that is also a advantages for mercury
to be used in thermometers however in
spite of so many advantages of mercury
there is one disadvantage which which is
being phased these days that mercury
being very poisonous it is very this
difficult to get disposed if by chance
the thermometer breaks therefore these
days a substitute of mercury has been
found and that is alcohol so a lot of
digital thermometers have come up and in
a lot of thermometers these days instead
of mercury alcohol is being used because
alcohol also has a very high coefficient
of expansion and at the same time it is
wrong the that poisonous as well
so with this thank you
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