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




On 2011, Sep 19, , at 13:11, 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?


Yes, and its square is the intensity -- both common terms in optics.




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




Reflection requires interaction w/ both free and bound electrons, gamma rays do so and are reflected, in the case of quasi free it's called the Compton and Thompson in both cases its more properly scattering and the angles are not necessarily equal.

And:

"Even hard X-rays and gamma rays can be reflected at shallow angles with special "grazing" mirrors."

Baez' disst. and further research was on this.

http://en.wikipedia.org/wiki/Albert_Baez


http://en.wikipedia.org/wiki/Reflection_(physics)

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In the case of bound electrons interaction peaks when the transition energy matches the photon's energy. Most gammas have a much greater energy than even K => transitions of high Z nuclei, so they are rather transparent

Of course, this is a simplified classical description, which is given in many optics texts, e.g. Jenkins and White -- look under dispersion (theory). this theory is analogous to the mechanical theory of Helholtz'

bc notes the most famous gamma ray (Mössbauer Fe-57) has only ~ 14.4 keV, well in the X-ray region.



Thank you.
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