SAT Subject Physics Practice Question 120: Answer and Explanation

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Question: 120

3. A beam of light in air is incident upon the smooth surface of a piece of flint glass, as shown

If the reflected beam and refracted beam are perpendicular to each other, what is the index of refraction of the glass?

D. 2
E. 2

Correct Answer: C


First, eliminate A and B: The index of refraction is never smaller than 1. Refer to the following diagram:

Since the reflected and refracted beams are perpendicular to each other, we have θ2 = 30°. Snell’s law then becomes

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