How to calculate speed of light with index of refraction?
Answers
The Speed of Light and the Index of Refraction
"Nothing can travel faster than the speed of light."
"Light always travels at the same speed."
Have you heard these statements before? They are often quoted as results of Einstein's theory of relativity. Unfortunately, these statements are somewhat misleading. Let's add a few words to them to clarify. "Nothing can travel faster than the speed of light in a vacuum." "Light in a vacuum always travels at the same speed." Those additional three words in a vacuum are very important. A vacuum is a region with no matter in it. So a vacuum would not contain any dust particles (unlike a vacuum cleaner, which is generally full of dust particles).
Light traveling through anything other than a perfect vacuum will scatter off off whatever particles exist, as illustrated below.
In vacuum the speed of light is
c = 2.99792458 x 108 m/s
This vacuum speed of light, c, is what the statements from relativity describe. Whenever light is in a vacuum, its speed has that exact value, no matter who measures it. Even if the vacuum is inside a box in a rocket traveling away from earth, both an astronaut in the rocket and a hypothetical observer on earth will measure the speed of light moving through that box to be exactly c. No one will measure a faster speed. Indeed, c is the ultimate speed limit of the universe.
Hope it will help you