Two small, flat patches of a soap film (index 1.33, surrounded by air on both sides)…
PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics
Problem
Two small, flat patches of a soap film (index 1.33, surrounded by air on both sides) are illuminated and observed at normal incidence. Patch A has thickness tA=180nm, and patch B has thickness tB=240nm. Both patches are viewed in white light.
Provide quantitative answers in the following parts.
(a) For each patch, determine the lowest-order visible wavelength that is constructively reinforced in the reflected light. List any additional visible wavelengths (up to 700nm) that are also reinforced for that same thickness.
(b) Using your results from part (a), predict which patch appears the brighter red to the observer. Support your choice with calculations or clearly articulated reasoning.
(c) Explain why the two patches do not look identical even though both involve constructive interference of multiple wavelengths.