Re: [Phys-L] Why is light slower in glass?

[John Denker <jsd@av8n.com>]

On 01/24/2016 09:51 PM, Bob Sciamanda wrote:
> The Sine wave, the Cosine wave and the resultant wave in this picture
> all travel  with the same velocity.  They are only out of phase with
> each other. A Sin(kx-wt) +B Cos(kx-wt) = RSin (kx-wt+Theta)

That's only one step in a multi-step argument.

The next step is this:  If you get /more and more/ phase
shift as a function of distance, then the resultant has a
different k vector for the same ω ... and (more specifically
and more importantly) a different dω/dk i.e. a different
group speed.