A dipole of dipole moment p is kept at the centre of a ring of radius R and charge Q. The dipole moment has direction along the axis of the ring. The resultant force on the ring due to the dipole is
Answer & explanation
Correct answer: option 2
$ F = p \frac{dE}{dx} $
$ E = \frac{kQ}{2{R^2+x^2}^{3/2}}$
$\frac{dE}{dx} _{ x= 0 }= \frac{kQ}{R^3}$
$\Rightarrow F = p \frac{dE}{dx} = \frac{kpQ}{R^3}$