Four point charges `+q,+q,-q and -q` are placed on the corners of a square of side length 'a' as shown in the figure. The magnitude of electric field at a point which is at a distance `x (gt gt a)` from the centre along a line perpendicular to the plane of the square and passing through the centre is

Answer

`(1)/(4pi in_(0)) (2sqrt(2)ql)/((l^(2)+x^(2))^(3//2))`