Four electric charges +q, +q, $$-$$ q and $$-$$ q are placed at the corners of a square of side 2L (see figure). The electric potential at point A, midway between the two charges + q and +q, is

The electric field at a distance $${{3R} \over 2}$$ from the centre of a charged conducting spherical shell of radius R is E. The electric field at a distance $${R \over 2}$$ from the centre of the sphere is

Two positives ions, each carrying a charge q, are separated by a distance d. If F is the force of repulsion between the ions, the number of electrons missing from each ion will be (e being the charge on an electron)

A square surface of side L meter in the plane of the paper is placed in a uniform electric field $$E$$(volt/m) acting along the same plane at an angle $$\theta $$ with the horizontal side of the square as shown in figurre.


The electric flux linked to the surface, in units of volt m is