# Homework Help: Conceptual Index of Refraction Question.

1. Dec 8, 2009

### fallen186

We have the index of refraction formula of $$n = \frac{c}{v}$$ which essential states how much of a factor light travels faster in a vacuum than in this medium. Why don't they just have it as $$n=\frac{v}{c}$$ so it states fractionally how much slower light travels in the medium than the speed of light.

Its like saying light in a vacuum is going 1.5 times faster than it would if it was in glass compared to "light going through glass is 2/3 slower than going in a vacuum".

I feel like it would be simpiler to just to say 2/3, and less confusing.

2. Dec 8, 2009

### Redbelly98

Staff Emeritus
I agree with you.

However, Snell's Law for the refraction of light predates the first reasonable measurement of the speed of light. The index of refraction was initially used to explain light refraction at an interface, and the speed of light was not a consideration in its definition.