The two coherent monochromatic light beams of intensities I and 4I are superposed. The maximum and minimum possible intensities in the resulting beams are:

9I and I

The correct answer is Option (2) → 9I and I

$I_{max}=(\sqrt{I_1}+\sqrt{I_2})^2$

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

$=9I$

$I_{min}=(\sqrt{I_1}-\sqrt{I_2})^2$

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

$=I$

$⇒\frac{I_{max}}{I_{min}}=\frac{9I}{I}=\frac{9}{1}$