Question

Two coherent light beams of intensities $I$ and $4I$ are suspended. The maximum and minimum possible intensities in the resulting beam are

• A. $5I$ and $I$
• B. $5I$ and $3I$
• C. $9I$ and $I$
• D. $9I$ and $3I$

Answer 1

The correct option is C $9I$ and $I$

We have:

$I_{res}=I_1+I_2+2\sqrt{I_1{I}_2}\cos \varphi$

$I_{max}={(\sqrt{I_1}+\sqrt{I_2})}^2{I}_{min}={(\sqrt{I_1}-\sqrt{I_2})}^2$

For, $I_2=4I$ and $I_1=I$, we have $I_{max}=9I$ and $I_{min}=I$