How to determine the frequency of EM wave which does not oscillate?

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Discussion Overview

The discussion revolves around determining the frequency of an electromagnetic (EM) wave produced by an accelerating charge in a vacuum. Participants explore whether the frequency depends on the speed of the charge and the nature of its acceleration, as well as the mechanisms involved in the production of EM waves.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests that the frequency of the produced EM wave may depend on the speed at which the charge moves and the amount of acceleration applied.
  • Another participant proposes using the Fourier transform to analyze the frequency components of the EM wave, indicating that it would contain an infinite number of frequency components.
  • A participant introduces three different mechanisms for EM wave production: Bremsstrahlung, synchrotron radiation, and free-electron lasers, each producing characteristic spectra and having different spectral distributions.
  • There is a request for clarification on the role of the charge's properties in the Fourier transform analysis, specifically questioning whether the rate of acceleration is significant.
  • One participant emphasizes that the Fourier transform is a general method applicable to various types of waves, not limited to electromagnetic waves or specific to charge behavior.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the mechanisms of EM wave production and the factors influencing frequency determination. The discussion remains unresolved with no consensus on the specific dependencies or mechanisms involved.

Contextual Notes

Participants mention different mechanisms for EM wave production, but there is no consensus on how these relate to the frequency of the waves produced. The discussion also highlights the complexity of the Fourier transform application without resolving the specific conditions or assumptions involved.

k9b4
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If I have a charge in a vacuum, and I accelerate it in a direction, then stop accelerating it, an EM wave will be produced for a short amount of time.

How can you determine the frequency of the EM wave which is produced? Does it depend on the speed at which the charge moves? The amount the charge accelerates?
 
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You would use the Fourier transform. It would contain an infinite number of frequency components.
 
k9b4 said:
How can you determine the frequency of the EM wave which is produced? Does it depend on the speed at which the charge moves? The amount the charge accelerates?

There are at least three different mechanisms, each producing their own characteristic spectra. Bremsstrahlung is produced by accelerations associated with collisions:

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

Synchotron (or cyclotron) radiation is associated with electrons traveling through magnetic fields:

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

Both of those have broad-band spectral distributions and can be characterized by routine measurement methods.

Free-electron lasers operate similarly to synchotron sources, but the magnetic field is spatially tuned (a 'wiggler') to provide a resonant interaction, resulting in narrow-band emission:

http://en.wikipedia.org/wiki/Free-electron_laser
 
DaleSpam said:
You would use the Fourier transform. It would contain an infinite number of frequency components.
Could you elaborate? What property of the charge is important in this Fourier transform? Is it the rate of acceleration of the charge?
 
Here is a link to the Wikipedia on the Fourier transform:
http://en.wikipedia.org/wiki/Fourier_transform

The Fourier transform is how you decompose any wave into its various frequency components. It has nothing specific to do with charge. It applies for EM waves, water waves, sound waves, and any other kind of waves you could imagine.
 

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