A thin film of MgF2 (n = 1.38) coats a piece of glass. Constructive interference is observed for the reflection of light with wavelengths of 450 nm and 563 nm .

n for glass is about 1.5

so the light undergoes a phase shift at both the top and bottom surfaces of the film

this means that we need a full wavelength path difference for constructive interference

since the light travels down and back up we need a film which is a whole number multiple of half wavelengths

now (450/2)*(563/2) = 63337.5

and 225 goes into that 218.5 times so we need twice that length to get a whole number multiple or 126675 nm

which is 126.675 micrometer

round appropriately

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This post is last updated on hrtanswers.com at Date : 1st of September – 2022