The wavefront is a surface in which

Two charges $$10 ~\mu \mathrm{C}$$ and $$-10 ~\mu \mathrm{C}$$ are placed at points $$A$$ and $$B$$ separated by a distance of $$10 \mathrm{~cm}$$. Find the electric field at a point $$P$$ on the perpendicular bisector of $$A B$$, at a distance of $$12 \mathrm{~cm}$$ from its mid-point.

When a number of charged liquid drops coalesce, which of the following quantity does not change?

What is the angle between maximum value of potential gradient and equipotential surface?