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

[John Denker <jsd@av8n.com>]

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.