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

[brian whatcott <betwys1@sbcglobal.net>]

On 9/19/2011 3:11 PM, Zeke Kossover wrote:
> Two questions
>
> 1. Would it be reasonable to say (that is, pedagogically a good idea) that an electromagnetic wave has an amplitude? 
>
> 2. Why are microwaves reflected by a piece of metal and not gamma rays? Don't both have a skin effect?
>
> Thank you.
As an effort to stir the pot, I offer this.

Anything that oscillates cycles energy between different forms. We take 
the amplitude to represent the difference between the greatest positive 
and negative displacements, at least for mechanical oscillators.
It seems that in the case of the pendulum, the other energy form  is 
kinetic, has a greatest value at the midpoint, and the v squared form 
makes it necessary to represent that energy amplitude as twice  the 
kinetic energy found for one sweep (??)

We suppose that an electromagnetic wave cycles magnetic and electric 
components (though I hear it is considered improper to represent this 
wave as cycling between modes, for some reason that escapes me) Here, we 
could provide an amplitude for the electric component, or for the 
magnetic component, it seems.

Light is reflected at a mirror surface, but largely traverses a clear 
glass. I can suppose that microwaves find considerably rougher metallic 
surfaces sufficiently reflective, but gamma waves can find smooth 
metallic surfaces sufficiently transmissive, except at shallow glancing 
angles, where the relevant interactions have enough proximity to provide 
some  reflection.

Brian W