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

$E_0 = 1.8\times 10^7~V/m$
We can find the intensity of the signal: $I = \frac{P}{\pi~r^2}$ $I = \frac{E}{\pi~r^2~t}$ $I = \frac{0.0025~J}{(\pi)~(0.425\times 10^{-3}~m)^2(10\times 10^{-9}~s)}$ $I = 4.4057\times 10^{11}~W/m^2$ We can find the electric field amplitude: $I = \frac{1}{2}~E_0^2~\epsilon_0~c$ $E_0^2 = \frac{2~I}{\epsilon_0~c}$ $E_0 = \sqrt{\frac{2~I}{\epsilon_0~c}}$ $E_0 = \sqrt{\frac{(2)(4.4057\times 10^{11}~W/m^2)}{(8.854\times 10^{-12}~F/m)~(3.0\times 10^8~m/s)}}$ $E_0 = 1.8\times 10^7~V/m$