Question

Two coherent monochromatic light beams of intensities $I$ and $4I$ are superposed. The maximum and minimum possible resulting intensities are :

• A. $5I$ and $0$
• B. $5I$ and $3I$
• C. $9I$ and $I$
• D. $9I$ and $3I$

Answer 1

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

Maximum intensity, $I_{max}=(\sqrt{I_1}+\sqrt{I_2}{)}^2$
$=(\sqrt{I}+\sqrt{4I}{)}^2$
$=9I$
Minimum intensity $I_{min}=(\sqrt{I_1}-\sqrt{I_2}{)}^2$
$(\sqrt{I}-\sqrt{4I}{)}^2$
$=I$