# Why does light slow down in denser media?

1. Sep 16, 2011

### ARAVIND113122

Why does light slow down when entering a denser medium? And why does it bend when it slows down?

2. Sep 16, 2011

### danielakkerma

Hi,
Since the interaction of light as a wave is governed by Maxwell's equations, they also predict that as light enters media different than vaccum, that has properties defined by such constant as a dielectric and magnetic permittivity and permeability respectively, $\epsilon_r, \mu_r$ altering the refractive index, $n = \sqrt {\epsilon_r \mu_r}$.
As light negotiates the denser atomic structure in media other than vaccum, via interactions on the atomic scale, it alters its directions due to a change in its phase velocity. To conserve the laws of propogation, i.e Huygens' and Fermat's principles(of "least time"), the light beam deflects. This is true, by-the-by, for any sort of Electromagnetic radation, and stirctly speaking, for any wave, as all might undergo diffraction and thus alter their parameters.
Hope that explains it simply enough,
Daniel

3. Sep 16, 2011