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When we study the interaction of the electromagnetic radiation with free electrons we can find two different approaches in the literature: for low frequency (RF, light...) a classical view is used and it is said that the electrons oscillates due to the electric field of the wave, but for high frequency radiation (X-rays, gamma), the type of interaction seems totally different (Compton effect and the like) and radiation is usually modeled as "particles". For a radiation with "intermediate" frequency such as UV or very low energy X-rays, would interactions be "electric-like" or "compton-like"?. How is the transition between both regimens?

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  • $\begingroup$ You have to realize that the classical view emerges from underlying quantum mechanical view (particles). Nature is really in its foundations quantum mechanical but it is practical to use classical theories and models in the macro state , i.e. dimensionswhere hbar is effectively equal to zero as far as measurements go. $\endgroup$
    – anna v
    Jul 27, 2013 at 19:02
  • $\begingroup$ I already assumed that, but how does exactly the classical oscillation emerge from particle-type (Compton) collisions? $\endgroup$
    – CFraggle
    Jul 28, 2013 at 11:23
  • $\begingroup$ i.e., what happens in the transition region (at an intermediate wavelength)? $\endgroup$
    – CFraggle
    Jul 28, 2013 at 11:30
  • $\begingroup$ Have a look at how classical fields emerge from quantum/particle ones: motls.blogspot.com/2011/11/… .you have to define intermediate region in debroglie wavelengths of the particle. Depending on the accuracy of measurement the particle/photon view will dominate of the classical em field/particle one. I think nano technology gives such orders of discrimination. watch the fuziness in these: youtube.com/watch?v=oSCX78-8-q0 . fuzziness is due to the qm uncertainties . $\endgroup$
    – anna v
    Jul 28, 2013 at 12:08
  • $\begingroup$ good question ! $\endgroup$
    – guru
    Aug 11, 2013 at 19:05

1 Answer 1

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Wave length.

When the wavelength is many times larger as the interacting particle, you use a field. When about the same size as the particle, field approach doesn't work that well, change to particles.

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  • $\begingroup$ Since the electron does not have a "size", the wavelength is always larger than the particle. Did you mean the wave associated to the particle?. Anyway, there should be a smooth transition between both kinds of behaviours or regimens. How is it possible taking in to account the differences between a classical oscillation an a compton collision? $\endgroup$
    – CFraggle
    Jul 27, 2013 at 17:48
  • $\begingroup$ there is the de Broglie wavelength for every particle: lamda=h/p , so there is always a wavelength to gauge whether it is practical to use classical or quantum em $\endgroup$
    – anna v
    Jul 27, 2013 at 18:59
  • $\begingroup$ But how do you determine the 'size' of the interacting particle? Electron itself is defined by a wave packet and uncertainty in position depends on the specific type of measurements made. $\endgroup$
    – guru
    Aug 11, 2013 at 19:08
  • $\begingroup$ After a few years I see that the question didn't get a satisfactory answer. Perhaps I was not able to explain the doubt correctly. We all know that when the wavelength of the radiation is very short the particle description is more useful, and for long wavelength the classical description is more convenient despite being an aproximation. But the question that remains unanswered is: what happens in the middle, for intermediate wavelengths. If we could change the wavelength of the radiation in a continuous way, what would we see in the intermediate region. $\endgroup$
    – CFraggle
    Oct 1, 2021 at 9:33

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