White light incident normal to a thin soap film with n = 1.34 reflects with an interference maximum at 684 nm and an interference minimum at 570 nm with no minima between those two values. What is the thickness of the soap film?

Question

Quizplus · Accepted Answer

The interference maximum occurs when the path difference is an integer multiple of the wavelength, and the minimum occurs when it is a half-integer multiple. The difference in path length for the maximum and minimum is half a wavelength in the film. Using the formula for thin film interference, the thickness can be calculated as t = (mλ_max - (m+0.5)λ_min) / (2n), where m is the order of the maximum. Solving gives t = 638 nm.

White Light Incident Normal to a Thin Soap Film with N