Expert: Philip A. Stahl - 11/22/2007

Question
Hello again!

I wanted to know that why there is variation in velocity of light when it enter from one medium to another.
and on what factor does this velocity depends?

Thanx!
Please support your answer with mathematical calculations!

Answer
Hello,

Okay, yes there IS a variation, when light transits from one medium to another. For example, there is a measured ' slow down' when transiting from a vacuum to a much more dense medium like glass.

The dependent factor here is the index of refraction for the medium to which it transits.

The index of refraction is itself defined:

n  =  (speed of light in vacuo)/ (speed in medium)

Thus, light always travels at its max. speed in a vacuum.

As an example, the speed of light in quartz (n = 1.458) is found from:

v =  c/ n  =   (3 x 10^8 m/s)/  (1.458) = 2.058 x 10^8 m/s

If this is not clear to you, please respond with another follow-up question. I prefer this as opposed to assigning me an  "8" rating for clarity - especially when you already give a "10" for knowledge (as in a previous response). This is inconsistent, since - if the answer were THAT unclear (and to me "8" is a BAD rating!) than how would you know that my knowledge was that good?

Just something to consider when you ask future questions.