How is the refractive index of a medium related to the speed of light ? Obtain an expression for refractive index of a medium with respect to another in terms of speed of light in these two media ?

Explanation

If medium 1 is vacuum or air medium 2 is glass, then the refractive index of medium 2 considered with respect to vacuum or air is represented as `mu_(21)=mu_(ga)=mu_("glass")`
Then `mu_(21)` is the Absolute refractive index of medium 2.
Hence `mu_("glass")=("speed of light in air / vacuum")/("speed of light in medium 2 (say glass)")=(c )/(v_(2))`
If we consider a light ray travelling from medium 2 to medium 1, refractive index of medium 1 with respect to medium 2 `= mu_(12)`.
`mu_(12)=("speed of light in medium 2")/("speed of light in medium 1")=(v_(2))/(v_(1))`