Re: [Phys-l] Amplitude in E&M

[Aburr@aol.com]

as usual jsd comes up with an excellent reply
 
Alex. F. Burr  

 
In a message dated 9/19/2011 5:40:40 P.M. Mountain Daylight Time,  
jsd@av8n.com writes:

On  09/19/2011 01:11 PM, Zeke Kossover wrote:

> 1. Would it be  reasonable to say (that is, pedagogically a good idea)
> that an  electromagnetic wave has an amplitude?

Sure.  Why not?

>  2. Why are microwaves reflected by a piece of metal and not gamma
>  rays? Don't both have a skin effect?

Both of those concepts -- skin  effect and specular reflection --
are derived within the approximation of  classical /continuum/ 
electrodynamics, where electricity is a continuous  fluid, and 
the medium creates some "resistivity".  That is a good  approximation 
for metals, provided the timescales and lengthscales are  large enough.

For the gamma rays, the timescales and lengthscales are  waaaay
too short to permit the continuum approximation.

There's a  nice discussion of "The Origin of the Refractive Index"
in  Feynman.

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