SP211
Worksheet 38
35.4-35.5: Interference from Thin Films, Michelson’s Interferometer
Problem 1
A thin lm of soap (n = 1.33) is surrounded on both sides by air (n = 1.00).
(a) What is the smallest nonzero thickness of the bubble such that light with a 625 nm wavelength will
destructively interfere in the reflection?
(b) What is the smallest thickness of the bubble such that light with a 625 nm wavelength will constructively
interfere in the reflection?
Problem 2
A thin film of acetone (n = 1.25) coats a plate of glass (n = 1.50). White light is incident normal to the
film. In the reflections, fully destructive interference occurs for 600 nm and fully constructive interference
occurs for 700 nm. What is the smallest possible thickness of the acetone film?
HINT: make a list of possible thickness to fulfill each of the two conditions, and look for the same thickness
in both lists.
Problem 3
One of the mirrors in a Michelson interferometer is moved 0.350 mm and a shift of 785 bright fringes is
observed. What is the wavelength of light producing the fringes?