Question

If the index of refraction of a lens is 1.5, how fast does light travel in the lens?

Answer 1

Answer:

C.

Explanation:

Answer 2

The speed of light in a material is given by:
$v= \frac{c}{n}$
where
$c=3 \cdot 10^8 m/s$ is the speed of light in vacuum
n is the refractive index of the material

The lens in this problem has a refractive index of n=1.50, therefore the speed of light in the lens is
$v= \frac{c}{n}= \frac{3 \cdot 10^8 m/s}{1.50}=2 \cdot 10^8 m/s$

And the correct answer is C).