Why do soap bubbles shimmer with rainbow colors?
Show answer & explanation
Answer: Light reflecting off the film's two surfaces overlaps
Light reflecting off the film's two surfaces overlaps ✓ — A bubble's wall is a thin film of soapy water, and light reflects off both its outer and inner surfaces. The two reflections overlap, so some colors reinforce while others cancel, and as the film thins and flows, the colors shift and swirl.
Water in the film splits light like a prism — A prism spreads light because it's thick and angled, but a bubble wall is thinner than a wavelength of light and curves evenly. Its colors come from overlapping reflections, which is why they change as the film thins.
The soap contains colored dyes — Soap is colorless, and a bubble made from clear soap still shows rainbows. The colors come from light, not pigment, which is why a patch turns dark just before the bubble pops, when the film gets too thin to reflect color.
More Physics in Daily Life questions
- In a warm office that already reads 26 C, which change can make people feel cooler without lowering the thermostat?
- Why might 26 C feel acceptable in a breezy naturally ventilated summer building but too warm in a sealed winter office?
- On a warm, humid day, why can a 27 °C room feel worse once your skin is sweaty?
- Why can moving air make a 27 C room feel cooler without changing the thermometer?
- Why can a desk beside a cold window feel chilly even when the thermostat across the room still reads 22 C?
- In the same 22 C room, why might someone who just climbed stairs feel warm while someone sitting in a T-shirt feels chilly?