1.

What is the minimum thickness of a thin film required for constructive interference in the reflected light from it? Given, the refractive index of the film = 1.5, wavelength of the light incident on the film = 600nm

Answer»

100 NM
300 nm
50 nm
200 nm

Solution :Condition for constructive interference is
`2mu t = [2n + 1](lambda)/(2)`
where ,n = 0, 1, 2, 3,...
For minimum THICKNESS, n = 0
`2mu t = (lambda)/(2)`
`rightarrow t = (lambda)/(4mu) = (600 xx 10^(-9))/(4 xx 1.5)`
= 100 nm


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