Video: Introduction to Electrostatic Potential and Capacitance Video Lecture - Class 12

hello friends this video on
electrostatic potential part 1 is
brought to you by exam feel calm no more
fear from example the topics to be
covered in this lesson are electrostatic
potential equipotential surfaces
relation between electric fields and
potential and electrostatic potential
energy so friends as you know we are now
studying electrostatics right so we have
already gone through the half of the
topics in which we discussed about
electric charges electric fields due to
different kinds of conductors at
different points so now we are starting
the next half of the chapter and we will
start it with electrostatic potential so
here is another new concept so we will
study about that so thinking as you all
are already aware by now that thinking
of the applications of electrostatics
you see so many things around yourselves
many of which I discussed in the
previous lesson so one of the best
example which you can think of is the
lightning flash which you observe almost
every day during rainy seasons right so
this is one of the very good examples of
electrostatics then we can talk about
the electric charges we can talk about
the electric fields and the electric
potential and also to some extent about
conductors but how it happens and what
actually happens we'll discuss that when
we reach towards the end of the lesson
so that it becomes easier for you to
understand that right so with this we'll
start our lesson on electrostatic
potential so this is again a new concept
so what is potential so from where does
this potential comes not I already told
you before that I already told you
before that electrostatics has some kind
of resemblance with gravitation right in
the previous lesson when we were talking
about the electrostatic force that is a
Coulomb's law it resembled a lot to the
gravitational
force right both of them looked similar
so before I introduce electrostatic
potential
I will first talk about gravitational
potential because gravitation is
something which we have already learned
in our previous class in a class xi we
have already studied about gravitation
so let me first start with gravitation
and then correlate electrostatic
potential with that with that -
gravitation so let us look at this this
is a ball which is lying on this table
what happens this ball reaches the
corner and then it falls down to the
ground why does this happen that's
because of the force of gravity so the
force of gravity is trying to push the
ball towards itself and that is why the
ball is falling to the ground okay but
as long as the ball was there at this
position it had potential energy so what
was the potential energy of the ball
when it was lying at this position this
is nothing but mg H hey height is so
basically that is potential energy right
which is due to its position or
configuration so here the ball has this
potential energy because of its position
from the surface of the earth correct
so this mg is nothing but it represents
the force which is exerted by the
surface of the earth the earth is
exerting this force on the ball and this
H is representing the height at which
the ball is located that is the position
of the ball so that is how we are
defining the potential energy and once
the ball starts falling down what
happens to the potential energy that
gets converted to the kinetic energy
right so when we talk about the
potential energy for this ball we assume
that the potential so when we talk of
this potential energy we assume that the
potential energy at the surface of the
earth is zero so here we consider
the potential energy has zero so as the
ball moves up above the surface so it it
attains some height right if it's
position gets defined by some height and
because of that it starts getting some
potential energy which gets stored in it
and as soon as it starts falling it gets
converted to kinetic energy right so
this concept is where is familiar with
you and you are well aware of it right
so now I will tell you about the
electrostatic potential energy and you
have to think it in the same lines now
let us suppose that instead of the earth
here you have some object with positive
charge let us suppose this this
resembles anything any conductor any
metal plate or anything some object with
positive charges so what whatever we
have learnt about charges what do we
know that like charges don't like each
other right so whenever there are light
charges they will try to repel they will
try to go away from each other now what
I do I bring this another small positive
charge in the periphery of this
positively charged conductor so what do
you think will happen will this positive
charge come towards the conductor and
stick to it no right so it will get
repelled by the positively charged
conductor and it will tend to move away
from the conductor right so it would
somewhat like this let us suppose these
are the electric field lines so this
charge by itself will have a tendency of
going away from the positively charged
conductor correct so what this this is
its natural tendency so what happens is
if you try to push it back if you
purposely want that this charge should
move towards the positively charged
conductor what do you need to do you
need to apply some extra force so very
similar to this scenario of ball for
example the ball if you don't do
anything the ball by itself will fall
towards the ground because the force of
gravity is already there but if you want
that it should not fall down
in that case you will have to apply some
extra force you will have to apply some
force and hold the ball right so only
when you apply some additional force it
will not move on its own right so in
that case how much force do you need to
apply so that the ball does not move to
the ground a minimum of a force equal to
this force which the earth is exerting
on the ball that minimum force is
required so that the ball does not go
down
similarly in this case because of the
electric field lines we have already
talked about electric field and field
lines right so because of the force due
to this these electric field lines this
charge will always have a tendency to
move towards right let us to move away
from this positively charged conductor
now if you want that this charge should
move in this direction that is towards
the left in that is you will have to
apply a force which is equal to at least
at least which has to be equal to the
force due to this electric field lines
so that means you are applying some
force on this particular charge let us
suppose this charge is Q it is a this
charge is Q let me write the English
draw all the forces that will become
easy see the force which is acting in
this direction that is the force due to
the electric field of this positively
charged conductor so if you want the
ball not to move in this direction
instead move in this direction so at
least you will have to apply a force
which is equal to F II in this direction
right so this has to be an external
force on this one so that means you are
doing some work to bring this charge
from this position to some position say
X wherever you are taking it so this
work which you are doing externally is
taking place opposite to the direction
of the electric field because the
electric field will attain
take this charge along with itself right
but you wanted to move opposite to the
electric field so you are applying an
external force and making it move in the
opposite direction so the work which is
done by you is nothing but that work
done is stored as potential energy in
this charge so what happens when you
apply this force the charge under this
force even though it is not willing to
go that side but since you are applying
that external force it has to move it
doesn't have any other option so let us
suppose it moves to some extent and as
soon as you leave the force let us
suppose you take it till this point X
and then you leave the external force
you don't give any force what will
happen to the charge will it stay there
no it will not because the charge
doesn't want to be here so it will
quickly accelerate and go back to its
original position that is that is it is
again go along with the electric field
so exactly similar to what happens in
gravitation in this case also first you
do a work that work is to - potential
energy right now as soon as you leave
the external force that potential energy
gets converted into kinetic energy and
that is when the charged particle again
moves back to its original position
right so this is how you can understand
the concept of electrostatic potential
energy comparing it with your
gravitational potential energy because
basically the concept of potential
energy still remains the same just that
your masses are now replaced by your
charges and there we talk about earth I
mean the force exerted by the earth here
the force is due to the electric field
lines that is the force due to the
electric field of some other charged
object because in electrostatics we will
basically deal with interaction of
different charges right so that was just
an introduction to tell you what are you
going to study in this lesson so this is
all about electrostatic potential energy
so now we will study everything that is
electrostatic potential energy
electrostatic potential potential
difference everything one by one thank
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