Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

$I = 2.0\times 10^{-5}~W/m^2$
The power spreads in all directions from the antenna. We can find the intensity at a point 10 kilometers away. $I = \frac{P}{A}$ $I = \frac{P}{4\pi~R^2}$ $I = \frac{25,000~W}{(4\pi)(10,000~m)^2}$ $I = 2.0\times 10^{-5}~W/m^2$