# 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”

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.

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.

Wow you are amazing!

What I have had trouble understanding this whole week you explained in a few minutes.

Thank you for doing this!

Really nice explanation there sir!

I missed this topic in class and found this, thanks a lot!

thanq sir

you've explained it very well within couple of minutes!! π

thank you

sir, how internal forces can apply torque

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

Sir

Why pΓE

Why not. EΓP

Plz explain

Sir you are really great .