Question

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

_______ m/s.

300 x 108
5.0 x 10-9
2.0 x 108
4.50 x 108

Answer 1

C.

Step-by-step explanation:

Answer 2

The speed of light in a material is given by:

`v= (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= (c)/(n)= (3 \cdot 10^8 m/s)/(1.50)=2 \cdot 10^8 m/s`

And the correct answer is C).