A glass plate (n=1.62) is coated with a thin, transparent film (n=1.27). Light r

Question

A glass plate (n=1.62) is coated with a thin, transparent film (n=1.27). Light reflected at normal incidence is observed as the wavelength is varied continuously. Constructive interference occurs for light at 680 nm, while destructive interference occurs at 544 nm (with no other incidences between these wavelengths).

a. Find the thickness of the film

b. If a different coating (n=1.7) is applied to the same thickness as you found in part (a) onto a clean sheet of the same glass, what, if any, visible wavelengths of light would show constructive interference?

Explanation / Answer

a) two low to his

2d = m*680

so m = 2d/680

2d = (m+1/2) 544

2d = (2d/680+0.5)*544

d =680 nm

b)

one low to high so constructive when

(m + 1/2) lambda = 2 d

lambda = 2*680/(m + 1/2) =

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