Chapter 16, Problem 4SP

A certain soap film has an index of refraction (see synthesis problem 1) of n = 1.4. This implies that the wavelength of light in the film is shorter than in air by a factor of 1/n. The index of refraction of air is approximately 1.0, so there is little difference between the wavelength in air and that in a vacuum.

a.    If light with an air or vacuum wavelength of 693 nm enters a soap film, what is the wavelength of this light in the film?

b.    If the film is 1980 nm thick, how many wavelengths farther does the wave reflected from the bottom surface of the film travel than that reflected from the top?

c.    Would you be surprised to find that this thickness produces destructive interference for reflected light?*