[QUE/EM-01013] --- EM-PROBLEM

A "dipole" is formed from a rod of length \(2a\) and two charges \(+q\)
and \(-q\). Two such dipoles are oriented as shown in figure at the end,
their centers being separated by a distance \(R\). Calculate the force
exerted on the left dipole and show that, for \(R>>a\), the force is
approximately given by
\[F=\frac{3p^2}{2\pi\epsilon_0R^4}\]
where \(p=2qa\) is the dipole moment.