Answer:
[tex]F = \frac{4kqQb}{(b^2 + \frac{d^2}{2})^{1.5}}[/tex]
Explanation:
Since all the four charges are equidistant from the position of Q
so here we can assume this charge distribution to be uniform same as that of a ring
so here electric field due to ring on its axis is given as
[tex]E = \frac{k(4q)x}{(x^2 + R^2)^{1.5}}[/tex]
here we have
x = b
and the radius of equivalent ring is given as the distance of each corner to the center of square
[tex]R = \frac{d}{\sqrt2}[/tex]
now we have
[tex]E = \frac{4kq b}{(b^2 + \frac{d^2}{2})^{1.5}}[/tex]
so the force on the charge is given as
[tex]F = QE[/tex]
[tex]F = \frac{4kqQb}{(b^2 + \frac{d^2}{2})^{1.5}}[/tex]