The potential energy U of an electric dipole of moment $p $ in an electric field $E$ is given by $U=−p .E$ and electric field due to $p $ at a point of position vector $r$ is given by $E=4πϵ_{o}r_{3}1 [3(p_{1} .r^)r^−p_{1} ],$ where $r$ = $rr^$ Now, consider two dipoles $p_{1} $ and $p_{2} $ ; the dipole $p_{1} $ is aligned along x - axis at the origin O (0, 0) and the dipole $p_{2} $ is kept at A (a,a). The minimum energy in terms of $U_{o}=8πε_{o}r_{3}p_{1}p_{2} $, of the dipole system is: