Soap bubbles show bands of rainbow colour on their surface. What produces this effect?
ALight is absorbed completely by the soap film
BLight is polarised as it enters the thin film
CLight is both refracted by and reflected from a very thin film
DLight is diffracted only at the very edge of the bubble
Answer & Solution
Correct answer: C. Light is both refracted by and reflected from a very thin film
1. The colours on a soap bubble occur when light is both refracted by and reflected from a very thin film.
2. Two reflected rays travel slightly different path lengths, so they end up out of phase with each other.
3. This phase difference causes interference, which reinforces particular wavelengths and produces the bands of colour.
4. Complete absorption would leave no light to see, and edge diffraction is a different phenomenon from this thin film effect.
_Source: OpenStax Physics (CC BY 4.0), Ch 15 "Light", section 15.2 The Behavior of Electromagnetic Radiation_
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