A narrow monochromatic beam of light of intensity 1 is incident on a glass plate as shown in figure Another identical glass plate is kept close to the first one and parallel to it. Each glass plate reflects `25%` of the light incident on it and transmits intensities in the interference pattern formed by two beams obtained after one reflection at each plate.

Answer

7

Explanation

`I` is the intensity of incident beam ab. The interfering waves are be and ef, reflected from surface of I and II plate, respectively.
Reflection coefficient of intensity.
`r = 5% = 0.25`
Transmission coefficient of intensity,
`t = 75% = 0.75`
The intensity of beam bc, `I_(1) = 0.25 I = (1)/(4) I`
The intensity of beam `bd = 0.75I`.
The intensity of beam `de = 0.25 xx 0.75 I`
The intensity of beam ef,
`I_(2) = 0.75 xx 0.25 xx 0.75 I = (9)/(64) I`
Ratio of maximum and minimum intensities,
`(sqrt I_(max))/(sqrt I_(min)) = (sqrt I_(1) + sqrt I_(2))/(sqrt I_(1) - sqrt I_(2)) = 7`