Chapter 31 - Electromagnetic Fields and Waves - Exercises and Problems - Page 901: 18

$I = 1.2\times 10^{-10}~W/m^2$

We can find the intensity of the smallest detectable signal: $I = \frac{1}{2}~E^2~\epsilon_0~c$ $I = (\frac{1}{2})(300\times 10^{-6}~V/m)^2 (8.854\times 10^{-12}~F/m)~(3.0\times 10^8~m/s)$ $I = 1.2\times 10^{-10}~W/m^2$