A thing coating (t=340 nm, n=1.480) is placed on a glass lens.Which visible (400

Question

A thing coating (t=340 nm, n=1.480) is placed on a glass lens.Which visible (400nm <<700 nm) wave length(s) will beabsent in the reflected beam if
(a) the glass has an index of refraction n=1.350
(b) the glass has an index of refraction n= 1.675

I don't know why I'm not getting the right answer. I thought thatthe condition for destructive interference for this case was(2nt)/ - 1/2 = m
Then I solved for and plugged in diferent values of m to seeat which visible wavelengths destructive interference occurs. Whatam I doing wrong?

Explanation / Answer

(a)the condition for interference in thin films is 2nt * cos(r) = (m - (1/2)) * or = [2nt * cos(r)/(m - (1/2))] m = 1,2,3,............... n = 1.480 t = 340 nm = 340 * 10^-9 m is the wavelength which will be absent in the reflectedbeam (b)similarly,when the index of refraction is n1 = 1.675then 1 = [2n1t * cos(r)/(m - (1/2))]

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