The figure shows equipotential surfaces due to two poit charges +3Q and -Q placed at a separation d.
(a) Will the shape of epuipotential surface be spherical very close to both the point charges? What shape of equipotentials will be seen at very far away points from the pair of charges. (b) Find the distance of point P from the negative charge. (c) Find the potential of the surface marked as `S_1` is the figure. (d) Consider the surface having zero potential. Write the flux of electric field through this surface