# SAT Subject Physics Practice Question 300: Answer and Explanation

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**Question: 300**

**71.**

Note: The figure is not drawn to scale.

The figure above shows a beam of light striking the surface of a piece of glass from the air.

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

A. sin 55°

B. 1/sin 55°

C. 1/sin 35°

D. sin 55°/sin 35°

E. sin 35°/sin 55°

**Correct Answer:** D

**Explanation:**

The diagram below (which *is* drawn to scale) shows that the angle of incidence, *θ*_{1}, is 55° and the angle of refraction, *θ*_{2}, is 35°.

Now by using Snell’s law, we find that