L9 : Polarization of Dielectric - Capacitor & Capacitance, Physics, Class 12 Video Lecture - Class 12 | Best Video for Class 12

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and capacitance part 9 this brought to
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before going ahead with path line let us
go and talk about and understand very
clearly what is polarization of a
damaged
now before we understand polarization of
a dielectric it is important to know the
different types of dielectric so there
will be classifications of dielectrics
that is there they are broadly two types
of dielectrics one is polar dielectrics
and the other one is non polar
dielectrics
now before we understand polar and
nonpolar dielectrics it is important to
remind you about what a polar and
nonpolar molecule it is I think most of
you must be knowing about it but still
less let me talk about movements we all
know that every molecule is made up of
atoms every atom has a nucleus and
electrons surrounding the nucleus the
nucleus has neutrons and protons protons
are positively charged and neutrons do
not have any charge so that means every
atom has some positive charges and some
negative charges now there is a center
of positive charge and the center of
negative charge when I say center of
positive charge that means the center
for all the positive charges and you
might be seeing that later suppose there
any number of positive charges so what
do you mean that you see the center of
positive charge Center positive charge
is nothing but the center of mass of
positively charged of all the positive
charges
similarly there is a center of mass of
all the negative charges so that is how
we have a center of positive charge and
a center of negative charge now if the
center of the positive and the negative
charges they coincide that is they are
along the same lines then we see the
molecule is no
polar right so in nonpolar molecule both
the Centers will coincide whereas in
case of a polar molecule the center of
positive charge and the center of
negative charge do not result for those
who already know this they would have
understood by now for those who are new
to this let me explain it motivated when
I talk about the lawn polar molecule non
polar molecule means the center of
positive and the center of negative
charges will coincide
for example if you look at your hydrogen
molecule if you look at your hydrogen
molecule this is the bond joining it
from center to center right so if you
look it from side wise you will look you
will see it like this if you look it
from front
it would look somewhat like this right
both the centers are I mean it is
something like you take two balls and
connect them from centers by some small
some small rod so how will it be if you
look it from front it will be as in the
centre of positive charge and this is
like above the center of negative charge
they exactly coincide with each other
right but when I talk about a polar
molecule in that case let us talk about
HCl so the center of positive charge it
is not exactly coinciding with the
center of negative charge I mean if you
see it from front they will not overlap
each other completely
they will look somewhat like this here
it is not completely overlapping right
the centre of the positive charge is
somewhere here whereas the centre of the
negative charge is somewhere here so it
is not getting overlap whereas in this
case the centre of the positive and
negative charges just coincided with
each other so when I look at a non-polar
molecule we are all symmetric but when I
look at a polar molecule they are not
symmetric because of that everything is
related to each other right
because the two molecules are not
click they are asymmetric that is why
the Centers of positive and negative
charges do not coincide right so you
understood polar molecule and nonpolar
molecule so when I talk about a polar
dielectric I means I mean to say a
dielectric which has polar molecules
similarly when I talk about a non polar
dielectric that means a dielectric
with non polar molecules correct now we
will see what happens if a polar
dielectric is placed in an external
electric field
I mean how will the electric field make
a difference now before that let us look
at a dielectric with polar molecules and
a dielectric with non-polar molecule
before external field is applied right
now I am just considering an dielectric
no electric field is applied here so let
us suppose this is my dielectric it has
all nonpolar molecules nonpolar
molecules means the positive center of
positive charge and negative charge
coincide so if this can be represented
somewhat like this they are all
spherical molecules because one sphere
above another sphere we completely
coincide each other so before the
external field is applied they look
somewhat like this when I look at a
polar molecule before an electric field
is applied they look somewhat like this
say this is positive charge this is
negative charge because they do not go
inside each other night so they are
separated by some distance so in this
polar molecules they are all randomly
oriented and now electric field is
applied so before an external field is
applied in case of a non polar molecule
since the positive and negative charges
are coinciding
so they are this day looking like this
whereas in case of a polar molecule they
are separated from each other because
they do not coincide now let us see what
happens when an external field is
applied so let us look at the non polar
molecule first so only your Q will
happen when an external field is applied
this centre of positive charge tends to
get attracted towards the negative
let us suppose the electric field is
applied I'm sorry let us suppose that
electric field is applied in this
direction positive to negative right so
now once the electric field is applied
what will happen the centre of negative
charge these negatives will get
attracted towards the positive and a
positive centre of positive will get
attracted towards the negative so
somewhat like this will happen the
centre of negative charges will tend to
be towards the positive charge of
external field and the centre of
positive charge we get aligned towards
the negative charge now let us see what
happens when external field is applied
to a polar molecule so in case of a
polar molecule toward you to see how was
it before before they were all randomly
oriented right but now once the electric
field is applied they all get oriented
in this way the negative charges are
come along the side whereas the positive
charges goes along the negative charge
of it so this is how the polar as well
as non polar dielectric behaves in
presence of electric field so what is
happening in presence of electric field
for both the molecules they are molecule
whether it is polar or nonpolar the
Centers of positive and negative charges
get separated from each other right and
as a result a small electric field is
induced inside as well but that field is
very less than the external field which
was applied and this is when we see that
a dielectric is cool next so when an
external field is applied the Centers of
positive and negative charges align
themselves in accordance with the
applied electric field and we see that
the dielectric is polarized so I hope
you understood now what do we mean by
polarization of a dielectric
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