A region of a soap bubble in air appears bright red (wavelength in air ) when viewed…
PHYSICS · Single correct · A Level · Physics · Waves · Waves
Problem
A region of a soap bubble in air appears bright red (wavelength in air ≈650nm) when viewed at normal incidence. Which of the following best explains the observation?
(a) The soap film thickness produces a half-wavelength path difference for red light, so the reflected red waves add while the other colors cancel.
(b) Because the film thickness is much smaller than blue and green wavelengths, those colors are not reflected, leaving predominantly red.
(c) The thickness at that spot gives a path difference that makes the reflected red light undergo constructive interference while most other visible wavelengths interfere destructively.
(d) The film acts like a tiny prism that disperses the colors and sends more red light back toward the observer than the other colors.