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?

A.
B.
C.
D. 2
E. 2

Correct Answer: C

Explanation:

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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