Permittivity and Permeability affect propagation velocity?

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Discussion Overview

The discussion revolves around the relationship between permittivity, permeability, and the propagation velocity of electromagnetic waves in different media. Participants explore whether these properties can account for changes in the speed of light, particularly in contexts like refraction and absorption.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that in refraction, the absorption and re-emission of photons contribute to light taking longer to travel through a medium.
  • Another participant references external sources stating that both permittivity and permeability affect the speed of wave propagation in a medium.
  • A participant questions whether there is anything unusual about permittivity and permeability that could explain an apparent change in velocity, similar to the effects seen in refraction.
  • One participant emphasizes that the speed of light in a medium is mathematically related to the product of permittivity and permeability, derived from Maxwell's equations.
  • A contribution from a participant with a background in physics confirms that the statements about permittivity and permeability are true and explains the relationship between these properties and the speed of light, including a discussion of scattering effects within a medium.

Areas of Agreement / Disagreement

Participants generally agree on the mathematical relationship between permittivity, permeability, and the speed of light. However, there is some uncertainty regarding the implications of these properties on the apparent change in velocity, and the discussion remains open to interpretation.

Contextual Notes

Some assumptions about the nature of light propagation and the effects of absorption and re-emission are present but not fully explored. The discussion does not resolve whether the external sources cited are accurate or if they adequately address the original question posed.

jmatejka
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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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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
 
Last edited:
jmatejka said:
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.
 
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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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