Answer
Choice C.
Work Step by Step
Use the formula given to find the maximum electric field.
$$E_{max}=\frac{350}{f}=\frac{350}{0.060kHz}=5800V/m$$
Now find the intensity for that maximum field.
The intensity of the light beam is $ I= \frac{1}{2}\epsilon_0 cE^2_{max}$.
$$ I= \frac{1}{2}(8.854\times10^{-12}F/m) (3.00\times10^8m/s )( 5800V/m)^2$$
$$ I= 4.5\times10^4 W/m^2$$
