Discussion Forum



1)

A parallel beam of light of intensity $I_{0}$ is incident on a coated glass plate. If 25% of the incident light is reflected from the upper surface and 50% of light is reflected from the lower surface of the glass  plate, the ratio of maximum to minimum  intensity  in the interference region of the reflected light is 


A) $\left(\frac{\frac{1}{2}+\sqrt{\frac{3}{8}}}{\frac{1}{2}-\sqrt{\frac{3}{8}}}\right)^{2}$

B) $\left(\frac{\frac{1}{4}+\sqrt{\frac{3}{8}}}{\frac{1}{2}-\sqrt{\frac{3}{8}}}\right)^{2}$

C) $\frac{5}{8}$

D) $\frac{8}{5}$

Answer:

Option A

Explanation:

 According to question , we can draw the following  diagram

1182021478_m10.PNG

  $I_{1}=\frac{I_{0}}{4} \Rightarrow  I_{2}= \frac{3}{8} I_{0}$

 We know that,

 $\frac{ I_{max}}{I_{min}}$= $\frac{(\sqrt{I_{1}}+\sqrt{I_{2}})^{2}}{(\sqrt{I_{1}}-\sqrt{I_{2}})^{2}}=\left(\frac{\frac{1}{2}+\sqrt{\frac{3}{8}}}{\frac{1}{2}-\sqrt{\frac{3}{8}}}\right)^{2}$