Incident Radiation (Part 2)

Electricity and Magnetism Level 4

In the $xyz$ -coordinate system, a thin solid square of side length $S$ lies in the $xy$ -plane with its center at the origin. An isotropic light source is positioned at $(x,y,z) = \left(0,0,\frac{S}{2}\right)$ .

What percentage of the light energy is incident on the square $($ to one decimal place; i.e., $66\frac{2}{3}\%$ would be entered as 66.7 $)?$