PhysicsLAB AP Free Response Question
2010 B5

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As shown above, a beam of red light of wavelength 6.65 x 10-7 meters in air is incident on a glass prism at an angle q1 with the normal. The glass has index of refraction n = 1.65 for the red light. When q1 = 40 degrees, the beam emerges on the other side of the prism at an angle q4 = 84 degrees.
 (a) Calculate the angle of refraction q 2 at the left side of the prism.

 (b) Using the same prism, describe a change to the setup that would result in total internal reflection of the beam at the right side of the prism. Justify your answer.

(c) The incident beam is now perpendicular to the surface. The glass is coated with a thin film that has an index of refraction nf = 1.38 to reduce the partial reflection of the beam at this angle.
 i. Calculate the wavelength of the red light in the film.

 ii. Calculate the minimum thickness of the film for which the intensity of the reflected red ray is near zero.

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