40. Class 12 Physics | Electric Potential | Electric Dipole Placed in a Uniform Field | Ashish Arora

# 40. Class 12 Physics | Electric Potential | Electric Dipole Placed in a Uniform Field | Ashish Arora

lets discuss. about what happen when electric
dipole is placed in, a uniform electric field. we know that uniform, electric field is a
situation where all electric lines of forces are. parallel and equi-distance from each
other. and here if we place a dipole just for, understanding in sake of simplicity i
am drawing, an enlarged we of a dipole. and say this is plus q and this minus q charge,
and this is the direction of dipole moment. which is placed. and dipole moment is making
an angle theta with the direction of, electric field vector. in this situation we know when
the dipole is placed in an electric field. the positive charge of dipole will experience
a force which is q-e in the direction of field. and negative charge being negative it’ll
experience a force q-e in the direction opposite to, the direction of field. and, as the dipole
itself is a system. and in all it is experiencing 1 force forward 1 backward so the net force
acting on the dipole in uniform electric field we can directly state it should be zero. must
be zero so we can say directly we can write. net force. on a dipole. placed, in a uniform.
electric field is this net force is equal to. zero. because, equal and opposite charges
will experience equal and opposite forces. but here we can see that these 2 forces are
not acting along this same line. so we can write. as. the 2 equal forces. are not acting.
along same line of action. these will produce. a couple. and we know that. the couple is
a torque. acting in the same direction due to both of these forces which is independent
of the. location of axis of rotation. so we can write down the value of torque as. in
case of couple it is defined as force multiplied by. separation between. lines of action of
forces. so here the magnitude of torque can be given as force which is q-e multiplied
by. the separation between the 2 lines here we can write as d sine theta because d is
the separation between charges and, theta is the angle between, the line joining charges
of dipole and electric field. so it’ll be d sine theta. and here we can write q d as
p so. torque can be written as p e sine theta where. p is the dipole moment, of this dipole
in electric field. and vectorially, this expression can be written as torque is equal to, p cross
e. both of these results are useful forever. for their applications. so just keep in mind
that. the torque acting on dipole depends on its dipole moment electric field and the
orientation of dipole that is the angle between dipole moment and the electric field.

## 10 Replies to “40. Class 12 Physics | Electric Potential | Electric Dipole Placed in a Uniform Field | Ashish Arora”

1. surbhi verma says:

explained very well.
but there is a mistake sir .when u write "[email protected]"
[email protected] comes because torque is a cross product.
and when put [email protected] the product sin 'X' should be removed.
where @ denotes thita
that's all sir..

over all video was fantastic.

2. Physics Galaxy says:

symbol X here denote times (or multiplication) it denotes cross product only when this symbol is used between two vectors. So there is no error here. For detailing and better sequencing of lectures you can follow these on site physicsgalaxy com.

3. Ariana Ateeq says:

Wow you are amazing!
What I have had trouble understanding this whole week you explained in a few minutes.
Thank you for doing this!

4. Abhinav Verma says:

Really nice explanation there sir!
I missed this topic in class and found this, thanks a lot!

5. Simran Kareer says:

thanq sir
you've explained it very well within couple of minutes!! 👍

6. Esraa Mohamed says:

thank you

7. Jagdish Kumar says:

sir, how internal forces can apply torque

8. Hinkiepunk says:

thank you sir, this helped me to understand in very few minutes

9. ejaz ahmad says:

Sir
Why p×E
Why not. E×P
Plz explain

10. jee aspirant says:

Sir you are really great .