• # question_answer A dipole has its moment $p$ is kept at the centre of a ring of radius R and charge q. The dipole moment has its direction along the axis of the ring. The resultant force on the ring due to the dipole is: A)  zero                             B)  $\frac{pq}{4\pi {{\varepsilon }_{0}}{{R}^{3}}}$ C)  $\frac{pq}{2\pi {{\varepsilon }_{0}}{{R}^{3}}}$                D)  $\frac{pq}{4\pi {{\varepsilon }_{0}}{{R}^{3}}},$ only if the charge uniformly distributed on the ring.

The electric field due to the dipole on the circumference of the ring, $E=\frac{P}{4\pi {{\varepsilon }_{0}}{{R}^{3}}}$ and it is directed normal to the plane charged ring. Hence, force on the charged ring             $F=qE=\frac{Pq}{4\pi {{\varepsilon }_{0}}{{R}^{3}}}$