White light is sent downward onto a horizontal thin film that is sandwiched between two materials. The indexes of refraction are 1.90 for the top material, 1.80 for the thin film, and 1.50 for the bottom material. The film thickness is 5.50 x 10-7 m. Of the visible wavelengths (400 nm to 700 nm), that result in fully destructive interference at an observer above the film, what is the longest wavelength?
a) 660 nm
b) 597 nm
c) 440 nm
d) 464 nm
e) 566 nm
Hint: What is the wavelength inside the film? For destructive interference, the path difference must be an odd number of half wavelengths.