The speed of light in a certain type of glass is 30% slower than the speed of light in air. What is the index of refraction for that type of plastic?
A) 1.33
B) 1.43
C) 1.5
D) 1.67

Question

Quizplus · Accepted Answer

The index of refraction is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium. Therefore, the index of refraction (n) of the glass is:
n = speed of light in vacuum / speed of light in glass
Since the speed of light in glass is 30% slower than in air, it is 70% of the speed of light in air. So we have:
n = speed of light in vacuum / (0.7 x speed of light in air)
n = 1 / 0.7
n = 1.43
Therefore, the answer is B.

The Speed of Light in a Certain Type of Glass