Inverse-square law

From Lauritz Thomsen's Wiki
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle I=\frac{\mathrm{P}_{source}}{\mathrm 4 \cdot \pi \cdot r^2}}