Point charges q and -q located at the vertices of a square with diagonals 2l as shown in figure. Find the magnitude of the electric field at a point located symmetrically with respect to the vertices of the square at a distance x from its centre. Consider `x gtgt l_(0)`
`[-(ql)/(sqrt(2)piepsilon_(0)x^(3))]`

Answer

`E=(ql)/(sqrt2piepsilon_(0)(l_(2)+x^(2))^(3//2))`