Problem 7

  In a certain time, light travels 3.50 km in a vacuum. During the same time, light travels only 2.50 km in a liquid. What is the refractive index of the liquid?

SOLUTION: The speed of light in vacuo is

$$c = \frac{3.50 km}{t} .$$

The speed of light in the liquid is

$$v = \frac{2.50 km}{t} .$$

Consequently, the index of refraction is

$$n = \frac{c}{v} = \frac{3.50}{2.50} = 1.40 .$$