Write the expression for torque experienced by an electric dipole in an uniform electric field. Give the meaning of the symbols used.

Explanation

Fore on -q of an electric dipole due to on electric fiedl E is `-qE`. And on `+q` is `+qE`.
These two forces are equal and opposite and act at A and B on the dipole. These forces constitute a restoring couple and maintains the position of the dipole in the field.
Torque `tau=` (Force ) (arm of the couple)
i.e. `tau=Fbar(AC)`
i.e. `tau=Fbar(AB) sin theta`
i.e. `tau=(qE)(2l)sin theta`
i.e. `tau=pE sin theta`
where `p=2lq` is called dipole moment.
`vec(tau)=p E sin theta hat n`
where `hatn` is unit vectro along `vect`
also `vec(tau)=vecpxxvecE`