Thin Film (Oil Slick)

# Thin Film (Oil Slick) - A scientist notices that an oil...

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A scientist notices that an oil slick floating on water when viewed from above has many different rainbow colors reflecting off the surface. She aims a spectrometer at a particular spot and measures the wavelength to be 750 (in air). The index of refraction of water is 1.33. Part A The index of refraction of the oil is 1.20. What is the minimum thickness of the oil slick at that spot? Hint A.1 Thin-film interference In thin films, there are interference effects because light reflects off the two different surfaces of the film. In this problem, the scientist observes the light that reflects off the air-oil interface and off the oil-water interface. Think about the phase difference created between these two rays. The phase difference will arise from differences in path length, as well as differences that are introduced by certain types of reflection. Recall that if the phase difference between two waves is (a full wavelength) then the waves interfere constructively, whereas if the phase difference is (half of a wavelength) the waves interfere destructively. Hint A.2

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## Thin Film (Oil Slick) - A scientist notices that an oil...

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