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Unformatted text preview: surface of a glass lens of refractive index n . The thickness t of the Flm is to be chosen so that light of wavelength 560 nm coming from air at normal incidence will undergo destructive interference in the re±ected waves. a. If n > 1.4 , what is the minimum non-zero value of t ? b. If n < 1.4 , what is the minimum non-zero value of t ? c. ²or the value of t in (a), there are other wavelengths (not in the visible region) for which destructive interference can occur in the re±ected waves. Are these wavelengths shorter or longer than 560 nm? Explain. a. In this case δ a = b = π so = 4 t ′ λ , where ′ = / n = 400 nm. The minimum t occurs when = , so we Fnd t = 100 nm. b. Now a = but b = so = 4 t ′ + . The smallest non-zero t occurs when = 3 , or t = 200 nm. c. The other cases have larger values of , so smaller values of . Physics 54 Summer 2011 2...
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This note was uploaded on 10/19/2011 for the course PHYSICS 54L taught by Professor Thomas during the Summer '09 term at Duke.
- Summer '09