in news:3bf8eeef@news.povray.org Warp wrote:

> Why does it go slower inside the
> object?
> 

From Maxwells third and fourth

c = 1/(E0*U0)^0.5

E0 = electric permittivity for free space
U0 = magnetic permittivity for free space

E0 = 8.85 x 10^-12 C^2 N^-1 m^-2
U0 = 4pi x 10^-7 Wb A^-1 m^-1

c = 2.999 x 10^8 m s^-1

In matter E0 and U0 become E and U
For most optical materials is nearnly equal to unity so that

n = c/v = E^0.5

From some very old notes from optics class.

Ingo

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