A short electric dipole (dipole moment P) is placed on the axis of a uniformly charged ring at a distance x from the centre as shown in figure. Radius of the ring is a and charge on it is Q.
Write the force on the dipole when `x=(a)/(2)` and when `x=a`. why the direction of force at two points is different?
(ii) is the force ont he dipole zero if `x=0` ? if not where will you place the dipole so that force on it is zero.

Answer

(i). At `x=(a)/(2);F=(16)/(5^(3//2))=(KQP)/(a^(3))`
at `x=a;F=-(KQP)/(2^(5//2)a^(3))`
(ii). No; force s zero at `x=+-(a)/(sqrt(2))`