A thin layer of oil (n = 1.25) is on top of a puddle of water (n = 1.33). If normally incident 500 nm light is strongly reflected, what is the minimum thickness of the oil layer?
A)200 nm
B)250 nm
C)100 nm
D)400 nm
E)150 nm

Question

Quizplus · Accepted Answer

The condition for strong reflection from a thin film is 2nt = mλ, where m is an integer, n is the index of refraction of the film, t is the thickness of the film, and λ is the wavelength of light. For m = 1 and λ = 500 nm, we have 2nt = 500 nm. Solving for t, we get t = 250 nm.

A Thin Layer of Oil (N = 1