Thin Film Interference
The colours in a bubble are not a rainbow, but are caused by interference of the reflected light waves.
A typical soap film is around one micron thick (one millionth of a meter). Light reflecting from the front and back surfaces of this film combines together. Depending on how thick this film is, different wavelengths (or colours) of light are reflected.
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The bubble in the photo is brightly lit from underneath so that all the light that you see is the reflected light, and is coloured. |
This same principle leads to the swirling colours of oil slicks on wet roads and is used in designing optics for lasers, colour filters for stage lights and anti-reflection coatings on glasses.
For an overview of some of the science at play inside a soap bubble, click here.
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