I was trying to show that in the field lines of the setup of two charges lets say $q_1$ and $q_2$ ,distance between then is $z$ where $q_1q_2 <0$ . We can always draw two imaginary spherical surfaces not necessarily with any one them acting as centre. Such that the electric field lines are always normal to the spherical surface.
My progress was that i wrote field equation , but i dont know how to show that a sphere is there or not . My main motto for showing the above fact was to show that from that : we can easily say that in a setup of a spherical conductor with a charge inside or outside we can always have the field lines inside/outside to be as if coming from a imaginary charge kept outside/inside the spherical conductor at some unique distance as a corollary which shows the method of images working .
