Effect of electrical permittivity on the speed of light?

[Muggo]

Why does an increased electrical permittivity reduce the phase velocity of light in a medium? Furthermore, what interactions do we see on an atomic level?

I am aware of the equation that defines the speed of light in terms of the electrical permittivity and magnetic permeability, but I do not understand their relationship.

Many thanks to anyone who is able to answer this question or/and refer me to a resource where I can obtain an answer!

 

[mfb]

Why does an increased electrical permittivity reduce the phase velocity of light in a medium?

If you construct wave equations out of the Maxwell equations, that is the result. Intuitively, it means the material reacts less to changes over time, which means the reaction becomes slower.

 

[tech99]

To take a mechanical analogy, consider a wave traveling on a taught string, as with a violin. The speed depends on the tension - the "desire" of the string not to be displaced - and inversely on the mass per unit length. Now consider a transmission line. Speed depends on tension, the voltage needed to impart a charge, which is the capacitance per unit length, and inversely on mass - the inductance per unit length. If we increase the permittivity, C is increased, so we can say that the tension is reduced and the wave slows down.
There is a good Wiki page on permittivity.