Question

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

• A. $5I\text{and}I$
• B. $5I\text{and}3I$
• C. $9I\text{and}I$
• D. $9I\text{and}3I$

Answer 1

The correct option is C $9I\text{and}I$

The maximum intensity is given by,
$I_{max}=(\sqrt{I_1}+\sqrt{I_2}{)}^2$

$=(\sqrt{4I}+\sqrt{I}{)}^2=9I$

The minimum intensity is,
$I_{min}=(\sqrt{I_1}-\sqrt{I_2}{)}^2$

$=(\sqrt{4I}-\sqrt{I}{)}^2=I$

Hence, $\left(C\right)$ is the correct answer.