A ray of light intensity I is incident on a parallel glass-slab at a point `A` as shown in figure. It undergoes partial reflection and refraction. At each reflection `25%` of incident energy is reflected. The rays `AB` and `A^(')B^(')` undergo interference. The ratio `I_(max)//I_(min)` is

Options

A. `4:1`
B. `8:1`
C. `7:1`
D. `49:1`

Answer

D

Explanation

`I_(1)=I//4, I_(2)=9I//64`
`I_(max)/I_(min)=((sqrt(I_(1))+sqrt(I_(2)))/(sqrt(I_(1))~sqrt(I_(2))))^(2)=((sqrt(I//4)+sqrt(9I//64))/(sqrt(I//4)-sqrt(9I//64)))^(2)`
`=((1/2+3/8)/(1/2-3/8))^(2)=(7/1)^(2)=49/1`