MCAT Physics Question 119: Answer and Explanation

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Question: 119

14. Imagine that a beam of monochromatic light originates in air and is allowed to shine upon the flat surface of a piece of glass at an angle of 60° with the normal. The reflected and refracted beams are perpendicular to each other. What is the index of refraction of the glass?

A.
B. 1
C. 2
D.

Correct Answer: D

Explanation:

Drawing a diagram is best here. Because the angle given is with respect to the normal, you know that the incident angle must equal 60°. You know that the reflected beam will have an angle of 60° relative to the normal. Therefore, the reflected beam will make an angle of 30° with the plane of the glass. If the reflected and refracted beams are perpendicular to each other, the refracted beam will make a 60° angle with the plane of the glass. θ_refracted is therefore 30° relative to the normal.

Using n₁ sin θ₁ = n₂ sin θ₂, we have

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