🚀 go-pugleaf

davids@spira.bri.hp.com (david sixsmith (contractor)) writes:

>1. What is (are) the inherent qualitie(s) of a substance, such as glass,
>perspex, diamond, & water, which make it transparent ?

The differential equation for an EM wave traveling in matter is given by
(For E only, a similiar equation holds for B):

\nabla^2 E = \ddot{E}/c^2 + \mu\dot{E}/\rho.

were \mu is the permeability and \rho the resistance per unit of length.
This equation has plane wave solutions:

E=E_0 exp(-\alpha x) cos(kx-\omega t)

here, k=\alpha=\sqrt{\mu\omega/2\rho}. So, if \alpha is small, the wave
can penetrate deeply wthout much absorption. This happens if \rho is large
(bad conductor, like glass and perspex, and/or \mu is small (usually approx 
\mu_r:=4\pi 10^{-7} H/m for this kind of materials).

>2. What is the mechanism which makes the speed of light lower when travelling
>in such a medium as opposed to traveling in a vacuum ?

The interaction between the photons and the atoms in the medium.

>This isn't in any way homework. Am I getting no response because no-one knows ?

I'm affraid you just asked the wrong people.
-- 
********************************************************** 
* J.C.A. Wevers                *   The only nature of    * 
* johan@blade.stack.urc.tue.nl *   reality is physics.   * 
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