States of Matter - Surface tension & energy Video Lecture - Class 11

hello friends this video states or back
about nineteen support you buy exactly
on call no more fear from exam before
watching the video please make sure that
you have watched part 1 part 18 let's
understand the concept behind surface
tension so if you see this water the
weight drops is like this see it forms a
spherical shape if you see it from
spiracle shape like this the question is
why why from spherical shape why not
square Y one treat angle 1 and Q PI and
Qi Y so if you see here oh so sometimes
you must have seen the waters in the
leaves they form shapes like this right
saved like this if it is in the air it
form shape like this
once it's dropped sometimes form shapes
like this also if you see if you have a
glass and if you put a light beam very
slightly not with force it will float it
won't go down but if you shake this
glass the spin may go down right what do
you put the spin very very gently it
will float why this floating why this is
spherically right why is this same do
here answer this do we know why this
happens this happens with the surface
tension will understand more of on
surface to the next like but these
things the pin floats the water in the
spherical shape the water table it will
take particular shape all without
superposition will understand the
surface tension that looks like so what
is surface tension surface tension is
nothing but property of water by the
virtue of fish the free surface of
liquid actually in liquid who is the
tendency to contract so as to acquire
minimum surface area Olympian once again
is the property of a liquid by the
virtue of which it tends to contract to
acquire millions of cases here why
because if you see if a let's suppose
the water is there is a water molecule
here it is attracted all sides equally
there is no net force on this
same thing applies for this guy but the
one in the surface if you see this
particular molecules is getting
attracted here but the net force exists
right because you see there is no force
from here there is a tension on this
right this guy's willing to come down
every every molecule in this thin down
to layer one should come down there's at
ancient Crete on this and this tension
creates a film kind of thing this is
found experimental this tension creates
a film kind of layer on this and on this
layer if you see but this is very this
layer is very gentle actually so if you
put this pin very gently it will float
but if you shake this it will come down
but there is a that is a very very thin
film kind of layer generated on this
surface because the surface tension
right so sub addition is what it is
nothing but the property of liquid to
contract to get the minimum surface area
and as the same reason why this droplet
of get this spherical shape because see
this droplet they want to have a minimum
surface area and if you calculate
mathematically sphere is the one which
has minimum surface area for a given
volume if I have it super volume is
constant so if you find for that volume
you find the if you make square if you
make cube I obviously make three
division thing if you make cube ID or if
you a cube or if you make sphere or if
you make cylinder you can do the KD of
the
three dimensional figure you'll find
that the cube you find the sphere has
the video surface area so it gets this
kind of shape minimizer surface area
right and I explained the molecules of
the surface explains net downward force
and have more energy than the molecules
here they have more energy more energy
they want to come down right and
therefore this liquids tend to have a
minimum number of molecules it is
because all these molecules are
suffering they are all happy these guys
all have happy molecules but these days
are all sad one
correct and though obviously if I'm a
family person right I want to make sure
every each of my molecules are happy
they want to minimize the number of
unhappy people here but somebody has to
be happy right somebody has to be in the
in the border they want to minimize the
number of people look number of
molecules are unhappy they always want
to minimize the surface area correct it
is you can say that in the country and
it's a border of the country these are
soldiers and they are unhappy normal
thing is they are happy so any country
want to minimize the number of unhappy
Sooni they want to do something that
surface the border is less right same
same thing here you can relate things to
the real life thing so this liquid want
to minimize the number of molecules the
surface area and how it can vary mines
by reducing the surface area itself
right and if you see here the the end of
the reason why we get this shape and if
you see the surface molecules get
attracted to the center and in this
surface layer of the molecules act as a
thin film there the protector the
protects are the molecule their thin
film on the that's why you see the spin
floats on this liquor correct surface
tension can also be defined in the force
acting per unit length perpendicular
line down on the surface over liquid you
have a salt film this is my moving this
is my movable movable rod so if I apply
some force on this right and this force
I move this film by existence right so
this forced surface tension we can also
define as the force acting per unit
length perpendicular to the line drawn
on the surface my fluid and it has to
film a clip to film so if I apply some
force on this and if you have the change
in this will be L into T into 2 y 2
because they are 2 socials 1 this side
another side so that force is nothing
but my surface area so you study more
about this
personal physics I think we have a big
chapter on a surface nation but it's
chemistry just understand that it is
required because in chemical reaction be
involved service ation and if you want
to know more about surface region you
can wash physics videos where the
surface tensions will explain in the
chemistry we'll learn not learn much
about it which may just learn that
there's a filtrated and with that film
you see this thing float and also if you
take this kind of structure where you
have this rod and this is a soap here
and you just pull this with the force
the total area of the so filling free
side but the soap we're all just trying
to minimize the area so it will set up
force and UX try apply the mixture force
and that is also called surface tension
correct and the magnitude of surface
tension depends on the attractive force
between the molecules the magnitude of
surface tension is a bedrock my tractive
force is attracting force is more
surface tension is large obviously
logical it makes sense right and if you
increase the kinetic energy of the
system the intermolecular force
attraction will decrease and thus if you
see the surface tension will decrease as
a temperature is raised so if you have a
glass and if you put one pin here
increase the temperature you see that
after some time it will come down
because the surface tension will
decrease on increasing temperature you
can do is experiment in your home you
can put this job or something one vessel
put some water in this put in the gas
storm and first put a pin here it will
float you heat it up then you see that
after some time this will come down
sorry surface tension is denoted by
Greek letter Gong and it has dimension
kg per second square and SI units called
Newton per meter all right
surface tension is also defined as
energy per unit area as I told
it is also defined as energy per unit
area and this with this you get a new
unit of surface tension there is Joule
per meter second Joule per meter square
so surface tension is either force per
unit length or energy per unit area
right both these are surface tension now
it's not about surface energy
see they toward the energy hair is more
than energy here right so if you see the
difference in energy this has more
energy this has small energy right big
and big and small e
so the energy difference between the
molecules at the surface and the
molecules of the poly and this surface
surface energy is nothing but surface
energy per unit surface area so the
energy you have here if you let suppose
you have some energy here divided by the
area of this that gives the surface
energy right energy by surface area and
the emission is Joule per meter square
right now they told the spherical shape
is because the lower surface energy
because the lower surface and the lowest
energy state of liquid is the surface
area is minimum right because see if you
have more molecules here it will a more
energy because the molecules in a higher
energy then you want to everybody want
to minimize the energy because energy is
stress right to the lowest energy state
of liquid will be and has lower surface
area and the spherical has shape has the
lowest surface area is plane that
mathematically if you see if you compare
for a given volume cube cuboid cylinder
spherical spherical and the lowest
surface area right also please note the
unit for surface energy is iron D reduce
surface tension because the fish nation
also I told you have to eat it in front
energy per area and this force per line
so the energy per area unit of the
supposition is similar to surface energy
and that's why we did it tell that the
surface energy and such
H done somewhere identical so you will
study more about submission area in
surface tension in physics or chemistry
that's all we should know just to clear
some doubts if we have victory in
surface tension surface energy let's see
the different between surface tension
surface energy the first thing is
surface tension has two units one is
Newton per meter and this force per
length or Joule per meter square
variance energy Bolivia but the surface
energy has only 1 in it
dual 1 Peter square surface tension is
measured along line they told if I have
some this kind of structure I have some
soap here you apply some force here the
whole place Basin across the line Bay
the surface energy is missing along an
area okay surface tension is nothing but
the net intermolecular force on the
surface molecules over liquid so I have
a liquid here some liquid on this
surface so the net force on these
molecules or the surface molecule is my
surface tension but the surface area
energy is nothing but the energy which
these molecules has right so in first
case I'm talking about the force
intermolecular force in chromoly I IMF
intermolecular force between the
molecules molecules or surface molecules
in case of surface energy I talk about
the energy in surface models hope you
understand a difference saying in this
surface tension I talk about the
intermolecular force between the surface
molecules in surface energy I talk about
the energy of the surface all right
thank you
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