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

From figure `I _(1) = (I )/(4) and `
`I _(2) = ( 9 I )/( 64) implies ( I _(2))/( I _(1)) = ( 9)/(16)`

By using
`(I _(max))/( I _(min )) = (( sqrt (( I _(2))/( I _(1)) ) + 1)/( sqrt (( I _(2))/( I _(1)))-1)) = (( sqrt (( 9)/( 16)) +1)/( sqrt ((9)/( 16))-1))^(2) = (49)/( 1)`