# Light from two sources , each of same frequency and travelling in same direction. but with intensity in ratio 4:1 interface. Find ratio of maximum to minimum intensity.

$(a)\;4:1 \\ (b)\;3:1 \\ (c)\;2:1 \\ (d)\; 9:1$

$\large\frac{I_{max}} {I_{min}}$$= \bigg(\large\frac{\sqrt {I_1}+ \sqrt {I_2}}{\sqrt {I_1}- \sqrt {I_2}}\bigg)^2$
$\qquad= \bigg[\large \frac{\sqrt {\frac {I_1}{I_2}} +1}{\sqrt {\frac{I_1}{I_2}}-1}\bigg]^2$
$\qquad=9:1$
Hence d is the correct answer.

edited Jul 23, 2014