A ray of light of internsity I is incident on a parallel glass slab at a point A as shown. It undergoes partial reflection and refraction. At each reflection and refraction. At each rerflection `20%` of incident energy is reflectrd. The rasys AB and A' B' undergo interference. The ratio `I_(max)//I_(min)` is

Explanation

According to the question, Intensity of ray `AB, I_(1)= (I_(0))/(5)` and Intensity of ray A'B'.

`I_(2)= (16I_(0))/(125), I_(max)= (sqrt(I_(1))+sqrt(I_(2)))^(2)= (81)/(125)I_(0)`
`I_(min)= (sqrt(I_(1))-sqrt(I_(2)))^(2)= (I_(0))/(125), (I_(max))/(I_(min))= 81` .