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AP Physics 2
14.9 Thin-Film Interference
IntermediateMCQMathematical17.6k
A diagram showing three horizontal regions stacked vertically. The top region is labeled Air with index n_1 = 1.00. Below it is a thin horizontal band labeled Gasoline of thickness t with index n_g = 1.40. Below the gasoline is a region labeled Water with index n_w = 1.33. An incident light ray arrow labeled \lambda travels downward through air at a slight angle to the vertical toward the air-gasoline interface. A first reflected ray arrow reflects upward back into the air from the top interface. A second ray continues downward into the gasoline, reflects upward off the gasoline-water interface, and travels back up into the air parallel to the first reflected ray. No other labels, lines, text, or axes appear.
Light reflecting from a thin film of gasoline on water.
A thin layer of gasoline with index of refraction \(n_g = 1.40\) floats on top of water with index of refraction \(n_w = 1.33\). Monochromatic blue light of wavelength \(\lambda\) in air shines nearly perpendicular to the surface of the gasoline film. The indices of refraction satisfy \(1.00 < n_w < n_g\). What is the minimum non-zero thickness \(t\) of the gasoline film that will produce constructive interference for the reflected light?

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