Index of Refraction

Definition: Index of Refraction, n:
With c = $\lambda$ f, we get: \[ \rm \mathbf{n = \frac{\lambda}{ \lambda_{m}}} \]
where $\lambda$_m = wavelength of light in medium (the frequency does not change by changing the medium)
=> Another form of Snell's Law: n₁ sin $\theta$₁ = n₂ sin $\theta$₂
By definition all indices of refraction are larger or equal 1, because the speed of light in media is smaller or equal the speed of light in vacuum.