Electromagnetic wave propagation

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Discussion Overview

The discussion revolves around the propagation of electromagnetic waves through a dielectric medium and the implications of transitioning to a vacuum. It explores theoretical aspects of wave speed, energy conservation, and frequency changes in different media.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant proposes considering a plane wave in a dielectric with specific properties and questions the effects of removing the dielectric on wave propagation.
  • Another participant asserts that the speed of the wave in empty space would be c.
  • A later reply confirms the speed as c but raises a question regarding the energetic implications of this transition.
  • One participant mentions the use of Fresnel relations to indicate that energy is conserved at the boundary, with some energy continuing and some being reflected.
  • Another participant notes that while the speed is c, the frequency of light remains unchanged in the medium, only the wavelength is affected, referencing the equation E=hf.

Areas of Agreement / Disagreement

Participants generally agree that the speed of the wave in empty space is c. However, there are differing views on the energetic implications and the effects on frequency and wavelength, indicating that the discussion remains unresolved.

Contextual Notes

There are limitations regarding assumptions about the properties of the dielectric and the conditions at the boundary where the transition occurs. The discussion does not resolve the implications of energy conservation in detail.

bernhard.rothenstein
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Please consider a plane wave that propagates through a dielectric with friendly properties (isotropic, non-conducting...) with speed c/n. What would happen if we remove the dielectric and the wave continues to propagate in empty space?
 
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Then speed = c.
 
e.m wave

Meir Achuz said:
Then speed = c.

Thanks. It is c but what happens from an enegetic point of view?
 
If the end of the dielectric is a flat face, use of the Fresnel relations show that energ is conserved. Some of the original energy continues, and some is reflected.
 
bernhard.rothenstein said:
Thanks. It is c but what happens from an enegetic point of view?

Interesting. Note that the frequency of the light does not change in the medium, only the wavelength. So, with E=hf...
 

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