The amplitude of the electric field of the wave in the problem is [tex]E=250 N/C[/tex].
The average intensity of the wave is related to the amplitude of the electric field by the equation
[tex]I= \frac{1}{2} c \epsilon_0 E^2 [/tex]
where I is the intensity, c is the speed of light and [tex]\epsilon_0[/tex] is the electric vacuum permittivity. By using E=250 N/C, we can find the average intensity of the wave:
[tex]I= \frac{1}{2}(3 \cdot 10^8 m/s)(8.85 \cdot 10^{-12} F/m)(250 N/C)^2=83.0 W/m^2 [/tex]
