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M4-21. Soap Film Interference - Simple Large Version


Very simple and clear demonstration of soap film interference.


Bright point source, wire loop with soap solution.

Setup Time

5 minutes.




A Bright point source of light at the right illuminates a soap film in the wire ring. The transmitted light is seen at the left and the reflected light at the rear between the transmitted light and the wire ring. Note that the ref lected and transmitted colors are complements. After a while the top section of the film becomes less than one-quarter wavelength thick, so the waves reflected from the front and rear surfaces of the film are out of phase, resulting in no reflected light .


David Lovett, Demonstrating Science with Soap Films, 204 pp., Institute of Physics Publishing, Philadelphia, 1994. ◙Goran Ramme, Colors on Soap Films - An Interference Phenomenon, TPT 28, 479-480 (1990).