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Credit: E. Wiebe

Thin film interference is a visually spectacular phenomenon of optics that unfortunately depends in this case on an environmentally damaging event. Spilled oil on wet pavement spreads out in a thin film on top of the water. The layer of oil gets progressively thinner as you move out to the edge of the spill. The presence of the thin film of oil means there are two reflective surfaces separated by a narrow (thin) gap. The light reflected from the top of the oil and water layers interferes, constructively and destructively, with itself. Where peaks in the waves line up they are made brighter and where troughs line up they are darker. Where peaks and troughs meet the particular wavelength is eliminated.

The result is a series of coloured bands or rings if the source is broad spectrum light, like the sun, or somewhat uniformly overcast sky in this case, where each coloured region represents a particular narrow range of wavelengths experiencing constructive interference while the others are reduced in intensity. The coloured bands represent regions of like thickness of the layer of oil. The colours repeat because the thickness is an integer mulitple of wavelength. This gives us the rainbow sheen effect that is so commonly seens as an indicator of a spill of oil.

Thin Film Interference on Wikipedia.

A vast amount of oil is leaked from poorly maintained vehicles every year. It's an amount comperable or greater than the largest point source oil spills. Moving our transporation systems away from carbon fuels won't completely eliminate spills since we still need to lubricate moving parts and the like but it will help to eliminate this source of pollution.




UVic / SEOS / Climate Group / About Front Page Picture / Thin Film Interference Last updated: Wednesday, 02-Jan-2013 10:20:03 PST
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