|MadSci Network: Other|
I probably have an advantage because I already knew the answer, but I also think it is possible that you could have found the answer if you used the Web. Doing a search on the terms: +"soap bubble" +interference +color on AltaVista I found this link to the Exploratorium, one of the most fascinating places in the World. It answers the question of where the colors come from. Here is an answer from another excellent site: How do oil spills/spots (i.e. in parking lots and streets) create rainbows? A thin layer of oil on water creates interference effects, just like those seen in a thin soap film. Sunlight reflects from both the top and the bottom of the oil layer and these two reflections can interfere with one another. If the blue/ green wavelengths of light interfere destructively on their way to your eye, you will see the oil layer as red. If the green/red wavelengths of light interfere destructively, you will see the oil layer as blue. How you see the oil layer depends on its thickness and the angles of the light. ***end of quoted material You may want to see if your bookstore or your library has this reference: The Science of Soap Films and Soap Bubbles. I got mine at Borders for $9.95. A real bargain because it has so much great stuff on optics and physics of soap bubbles. The black area that you mention occurs when the thickness of the bubble is less than 300 angstroms. This is less than the wavelength of visible light so no interference effects can create the colors that thicker films allow. David Winsemius, MD
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