A narrow monochromatic beam of light of intensity I is incident on a glass plate as shown in Fig. 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 the remaining. Find the ratio of minimum and maximum intensities in the interference pattern formed by the two beams obtained after one reflection at each plate.
Text Solution
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Sol. At each surface reflection and transmission takes place. Intensity of reflected and transmitted rays at first plate is I/4 and 3I/4 respectively. Incident intensity at second plate is 3I/4 respectively. Incident intensity at the second plate is 3I/4; 25% of it is reflected and 75% is transmitted. Intensity of reflected and transmitted rays at second plate is 
, 
respectively. The reflected rays from second plate reaching first plate are incident at first plate.
The reflected and transmitted intensities are 3I/64 and 9I/64.
As I max = ( 
+ 
) 2 = I 0 
= 
I 0
I min = ( 
– 
) 2 = I 0 
= 
I 0
Hence 
= 
= 
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