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    Interference of light: Thin air film between glass plates

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    Two Glass Plates (see attached file)

    Two glass plates are separated by fine wires, with diameters d1 = 0.0510 mm and d2 = 0.0530 mm, as indicated in the figure below. The wires are parallel and separated by a distance of L = 6.89 cm. If monochromatic light with lamba = 577 nm is incident from above, what is the distance (in cm) between adjacent dark bands in the reflected light? (Consider interference only between light reflected from the bottom surface of the upper plate and light reflected from the upper surface of the lower plate.)

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    Solution Preview

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    As the diameter of the two wires is different it makes a wedge shape air film between the two plates. The thickness of this air film is changing with the distance from one wire to the other. The light incident on the upper surface is partly reflected and partly refracted. Refracted light is again partly reflected from the lower interface of the film. Reflection takes place at both surfaces of this air film and thus we have two beams of reflected light in the region above the plates
    1. The light reflected from the upper surface of the film, and
    2. The ...

    Solution Summary

    The distance between the dark and bright bands is calculated for the interference due to reflections from thin air film.