Answer:
[tex]\sqrt{2} E[/tex]
Explanation:
The intensity of an electromagnetic wave is proportional to the square of the amplitude of the electric field:
[tex]I\propto E^2[/tex]
where
I is the intensity
E is the amplitude of the electric field
Therefore, considering the two waves of the problem, we can write:
[tex]\frac{I_1}{E_1^2}=\frac{I_2}{E_2^2}[/tex]
where
[tex]I_1 = 20 W/m^2[/tex] is the intensity of the first wave
[tex]E_1=E[/tex] is the electric field amplitude of the first wave
[tex]I_2 = 40 W/m^2[/tex] is the intensity of the second wave
[tex]E_2[/tex] is the electric field amplitude of the second wave
Solving for [tex]E_2[/tex],
[tex]E_2 = E \sqrt{\frac{I_2}{I_1}}=E\sqrt{\frac{40}{20}}=\sqrt{2} E[/tex]
