A puddle of water (n = 1.33)is covered with a very thin layer of oil (n = 1.20).How thick is the oil in the region that strongly reflects light with a wavelength of 550 nm?
A)207 nm
B)229 nm
C)458 nm
D)550 nm

Question

Quizplus · Accepted Answer

The condition for constructive interference in thin film is given by:
2nt = (m+1/2)λ
where n is the refractive index of the medium, t is the thickness of the film, λ is the wavelength, and m is an integer (0, 1, 2, 3,...).
For the reflected light with a wavelength of 550 nm in the oil film on water, m = 0 and we have:
2nt = λ/2
t = λ/4n
Substituting the values of n and λ, we get:
t = (550 nm)/(4×1.20) = 229 nm
Therefore, the thickness of the oil in the region that strongly reflects light with a wavelength of 550 nm is 229 nm, which is closest to option B.

A Puddle of Water (N = 1