Question #9c493

2 Answers
Apr 18, 2016

It will not change path if it is incident along the normal


When light moves from say air into glass, if its angle of incidence is #0^0# (i.e. it is along the path of the normal), then the light will slow down but not change path

Apr 18, 2016



It depends on what you call the "speed of light".

Being an EM wave, it has two definitions of velocity.

  1. Phase velocity :

Given as the velocity with which the phase front of the EM wave moves, This is the regular "velocity" we talk about. In space it is #3xx10^8 " m/s"#. And in any medium it is decreased by a factor of #mu# which is the refractive index of the medium. Now, since in most medium with high #mu# absorbs light as well, it has hard to "see" light wave propagating slowly.

2 . Group velocity:

This is how the "shape" of the wave travels.

enter image source here
By Geek3 - Own work;This mathematical image was created with Mathematica, CC BY 3.0,

Now depending on how the medium "reacts" to an incident light wave, this velocity can be decreased, and a beam has actually been stopped.

Interesting video: enter link description here

There you go .. it can be "slowed down", a lot .

Thank you for asking this.