Velocity of electromagnetic waves in a medium

[Geocentric]

# It is said that the velocity of electromagnetic waves in a medium depends upon the mechanical and electrical properties of a medium. Is it true? But the expression to find the velocity of electromagnetic waves in a medium = 1/(M)(E) says that it depends upon the electrical & magnetic properties of a medium. Please clear my doubt. Here M = permeability of medium and E = Permittivity of medium.

[Tim_Lou]

[math]c=\frac{1}{\sqrt{\epsilon\mu}}[/math]

from physicsworld.wolfram.com

http://scienceworld.wolfram.com/physics/SpeedofLight.html

 

this can be derived directly from maxwell's equations.

 

the thing is, in most materials that light can pass through, the magnetic permeability do not vary that much (glasses and gases usually do not become magnetized), hence in a sense it depends mostly on electric permittivity.