Problem 3.7

Point charges $q$ and $-q$ are located at the vertices of a square with diagonals $2 l$ as shown in Fig. 3.1. Find the magnitude of the electric field strength at a point located symmetrically with respect to the vertices of the square at a distance $x$ from its centre.

E=\frac{q l}{\sqrt{2} \pi \varepsilon_{0}\left(l^{2}+x^{2}\right)^{3 / 2}}

Constant Electric Field in a Vacuum