# Permittivity and Permeability affect propagation velocity?

#### jmatejka

If I understand correctly in refraction, photon absorption and re-emission accounts for light taking "longer" to travel.

Regarding Permeability and Permittivity, the below linked website states:

"permittivity affects the speed of propagation of a wave through a medium"

http://www.antenna-theory.com/definitions/permittivity.php

AND

"permeability also affects the speed of propagation of an electromagnetic wave in a medium"

http://www.antenna-theory.com/definitions/permeability.php

Googling didnt lead me to any supportive information, do the statements make any sense?

Thanks, John

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#### jmatejka

I am aware of the speed of light, my question is if anything unusual is going on with permittivity and permeability that could account for "apparent" change in velocity, as refraction does.

I also hopefully understand refraction is dealing with the photon and my question pertains to E&M fields.

If you believe the page to be in error please say so, Thanks, John

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#### voko

I am aware of the speed of light, my question is if anything unusual is going on with permittivity and permeability that could account for "apparent" change in velocity, as refraction does.
If you followed the link, it should be pretty obvious that the speed of propagation is directly related to the product of the quantities in question. If that is not what you are looking for, then I have no idea what you are asking about; you may want to rephrase your question.

#### jmatejka

If anyone is interested, below is a reply to my question from my friend Richard Blade, former Chair of the Physics Dept, University of Colorado at Colorado Springs:

John-

All the statements you quoted are true. Macrosopically and mathematically, the speed of light in a transparent medium is one over the square root of the product of the permittivity and the permeability. That comes about by deriving the wave equation from Maxwell's equations. From the microscopic view, you can imagine that the incident EM wave is being scattered inside the medium, and that the scattered wave is slightly delayed from the incident wave, thereby making the composite wave front slightly slower (during the period of absorption and re-emission) than the incident wave front. The math, although looking quite different, predicts exactly the same reduction in speed as the macroscopic.

Richard

This seems to be an elaboration to what was stated above by Voko. Thanks, Regards, John

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