A vertical soap film ( ) in air is viewed in reflected light
PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Interference and diffraction · Interference and diffraction
Optics and Photonics, Ch Multiple-beam interference: thin films, multilayers and the Fabry-Perot etalon
Problem
A vertical soap film (nf=1.33) in air is viewed in reflected light. Consider the component of vacuum wavelength λ=550 nm, incident from air at θi=45∘ from the normal.
((a)) Use Snell's law to find the angle of refraction θt inside the film.
((b)) Using the reflection phase change at each surface (front reflection external, back reflection internal, Chapter 6) together with the oblique path-difference formula Λ=2nfdcosθt, find the smallest film thickness d for which this wavelength is bright in reflection.