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Bubbles
Cluster of soap bubbles.
A variety of beautiful colors appear in the swirls. Often, just before bursting, the swirls will appear black.
A really long bubble. David Stein holds the official Guinness Book of Records mark for the longest bubble, over 15 m long.
The principle of interference, in which light reflected from a lower surface interferes with light reflected from an upper surface, is also seen in soap bubbles.
When an incoming ray of light strikes the outer surface of a bubble, part of the light ray is immediately reflected, while the other part is transmitted into the soap film. After reaching the inner surface of the film, this transmitted light ray is reflected back toward the outer surface. When it leaves the bubble, it travels in the same direction as the ray that was immediately reflected and is, therefore, parallel to that ray. If the two rays of light are reflected back so that their wavelengths are "out of phase" with each other, the second ray will partly cancel out the reflection of the first ray. This is called destructive interference and the result is a reduction in color intensity. If, however, the wavelengths of the two reflected rays are "in phase", they will enhance each other. This is called constructive interference and it produces iridescent color. Whether the rays are in or out of phase with each other depends on the amount of added distance through the film that the second ray must travel before joining the first ray back on the surface.
