Q. Two beams of light of intensity $I_{1}\ and\ I_{2}$ interfere to give an interference pattern. If the ratio of maximum intensity to that of minimum intensity is $\frac{25}{9},\ $then $\frac{I_{1}}{I_{2}}$ is
A) 5/3
B) 4
C) $\frac{81}{625}$
D) 16
Explanation
(d) $\frac{I_{\max}}{I_{\min}} = \frac{25}{9}$
$Or\ \left( \frac{a_{1} + a_{2}}{a_{1} - a_{2}} \right)^{2} = \frac{25}{9}$
Where $a$ denotes the amplitude.
Or $\frac{a_{1} + a_{2}}{a_{1} - a_{2}} = \frac{5}{3}$
Or $\frac{a_{1}}{a_{2}} = 4$
As, $(amplitude)^{2} \propto intensity$
Hence, $\frac{I_{1}}{I_{2}} = \left( \frac{a_{1}}{a_{2}} \right)^{2} = 16$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.