PhysicsLAB AP Free Response Question
2009 B5 Form B

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A wide beam of white light is incident normal to the surface of a uniform oil film. An observer looking down at the film sees green light that has maximum intensity at a wavelength of 5.2 x 10-7 m. The index of refraction of the oil is 1.7.

 (a) Calculate the speed at which the light travels within the film.

 (b) Calculate the wavelength of the green light within the film.

 (c) Calculate the minimum possible thickness of the film.

(d) The oil film now rests on a thick slab of glass with index of refraction 1.4, as shown in the figure below. A light ray is incident on the film at the angle shown. On the figure, sketch the path of the refracted light ray that passes through the film and the glass slab and exits into the air. Clearly show any bending of the ray at each interface. You are NOT expected to calculate the sizes of any angles.

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