Question

If a sinusoidal electromagnetic wave with intensity 18 W/m2 has an electric field of amplitude E, then a 36 W/m2 wave of the same wavelength will have an electric field of amplitude?
a. 4E
b. 2 underroot 2E
c. 2E
d. underroot E

Answer 1

Answer:

The  correct option is D

Explanation:

From the question we are told that

  The intensity of the first  electromagnetic wave is  $I = 18 \ W/m^2$

  The amplitude of the electric field is  $E_{max}_1 =A$

   The intensity of the second electromagnetic wave is  $I = 36 \ W/m^2$

Generally the an electromagnetic wave intensity is mathematically represented as

       $I = \frac{1}{2} * \epsilon_o * c * E_{max}^2$

Looking at this equation we see that

     $I \ \ \alpha \ \ E^2_{max}$

=>  $\frac{I_1}{I_2} = [ \frac{ E_{max}_1}{ E_{max}_2} ] ^2$

=>   $E_{max}_2 = \sqrt{\frac{x}{y} } * E_{max}_1$

=>  $E_{max}_2 = \sqrt{\frac{36}{18} } * E$        

=>  $E_{max}_2 = \sqrt{2 } E$