Frequency of Radiating EM Waves from a Moving Electron on a Unit Circle

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Discussion Overview

The discussion revolves around the frequency of electromagnetic (EM) waves radiated by an electron moving in a circular path, specifically on a unit circle. Participants explore the theoretical implications of this motion using Maxwell's equations, as well as the characteristics of the emitted radiation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests starting the analysis by using Maxwell's equations to derive the frequency of the radiating EM waves, questioning the known variables such as current density and charge density.
  • Another participant proposes calculating the frequency (omega) directly from the electron's velocity and radius, indicating a more straightforward approach.
  • A participant expresses a desire to derive the frequency rather than simply calculate it, indicating a preference for a more theoretical exploration.
  • It is noted that an electron can maintain circular motion only if a tangential force is applied, which leads to the conclusion that the radiation emitted will be circularly polarized, with the electric field spinning at the same frequency as the electron's revolution.
  • Another participant counters that the radiation is circularly polarized only when viewed along the axis of the loop, while radiation in the plane of the loop is linearly polarized.
  • A further clarification is made that the radiation is elliptically polarized in general, with specific characteristics depending on the observation angle.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the polarization of the emitted radiation, with some asserting circular polarization under certain conditions and others arguing for linear or elliptical polarization depending on the perspective of observation. The discussion remains unresolved regarding the definitive characteristics of the radiation.

Contextual Notes

There are limitations in the assumptions made regarding the forces acting on the electron and the definitions of polarization types, which have not been fully explored or resolved in the discussion.

qoqosz
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Let's assume that electron is moving around the unit circle. Using Maxwell equations show what is the frequency of radiating EM waves.
How to start with it? What's the form of known variables - current density and charge density?
 
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If all you want is the frequency, calculate omega from the electron's velocity and the radius.
 
I know that, but I'd like to derive it somehow.
 
An electron can travel in a circle, at a constant speed, only if it is driven by a tangential force that points in the same direction as the instantaneous velocity. The power expended by that force is constant, and thus the radiation can only be circularly polarized. You can solve for the electric field at some point above the circular orbit's center and will find that E spins about that line with the same frequency as the frequency of electron revolution.
 
Well, it's circularly polarized only if you look at it directly along the axis of the loop. The radiation in the plane of the loop is of course linearly polarized.
 
Ok, thanks.
 
conway said:
Well, it's circularly polarized only if you look at it directly along the axis of the loop. The radiation in the plane of the loop is of course linearly polarized.

It's "elliptically polarized" (if you prefer) everywhere. In the orbital plane the minor axis goes to the minimum limit of zero.
 

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