Why do electromagnetic waves reflect

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Discussion Overview

The discussion centers on the phenomenon of electromagnetic wave reflection and diffraction when encountering surfaces. Participants explore theoretical explanations, empirical observations, and the applicability of established laws such as Fresnel's equations in different contexts, including transparent and opaque materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion over the lack of analytical explanations for why electromagnetic waves reflect and diffract, despite their understanding of retarded potentials.
  • Another participant points out that classical Maxwell theory provides a theoretical framework through boundary conditions at the interface of different media, leading to laws of refraction and reflection.
  • References to Fresnel formulae and equations are made as a means to understand reflection and refraction in transparent media.
  • A participant questions how classical explanations, such as those provided by Fresnel's laws, apply to reflection from opaque objects, suggesting a need for modification in understanding.
  • One participant introduces the concept of plasma frequency in relation to reflection from surfaces, indicating that the frequency of incident light relative to plasma frequency determines whether it is transmitted or reflected.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as there are multiple competing views regarding the mechanisms of reflection and diffraction, particularly in the context of different materials (transparent vs. opaque).

Contextual Notes

Some discussions reference specific theoretical frameworks and empirical observations, but limitations include the lack of detailed analytical derivations for certain cases and the dependence on material properties such as plasma frequency.

HomogenousCow
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I have seen the retarded potentials and what not, but what has always bothered me is why these field solutions reflect when they meet surfaces.
I have looked and looked, but there seem to be no analytical explanations for this, only empirical ones.
So my gripe is, since electromagnetic waves are nothing but EM fields, why do they reflect and diffract.
 
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The theoretical explanation within classical Maxwell theory is that the fields must fulfill boundary conditions at the surface where two media join each other. From this you get, e.g., the laws of refraction and reflection in transparent media (dielectrics). This is treated in textbooks on electrodynamics and/or optics. Look for "Fresnel formulae".
 
vanhees71 said:
Look for "Fresnel formulae".

Or "Fresnel equations". A Google search for that term gives many hits. Some include derivations from Maxwell's equations.
 
Doesn't anyone want to ...(oh never mind)...
 
jtbell said:
Or "Fresnel equations". A Google search for that term gives many hits. Some include derivations from Maxwell's equations.

Fresnel's Laws apply to transparent materials. What about reflection from opaque objects ?
In post #3 above I reference a post by Antiphon. How would this classical explanation apply
or be modified for reflection from opaque object : Incidence = Absorbed+Reflected
 
Last edited:
reflection from a surface or refraction has it's basis in the material itself.it is related to the plasma frequency of the metal.if the light which falls on a surface has frequency greater than plasma frequency will be transmitted but lower will be reflected.these things belong to solid state physics.you can see, kittel for it and also feynman lectures vol.2(last 1/4 of book).Also here is a link http://en.wikipedia.org/wiki/Plasmon
 

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