Magnetic field of charge moving at constant velocity

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Discussion Overview

The discussion centers on calculating the magnetic field produced by a single charge moving at a constant velocity, examining both current and displacement current terms. Participants explore the implications of this scenario within the context of classical electromagnetism, particularly contrasting non-relativistic and relativistic frameworks.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants seek to understand the magnetic field of a moving charge in a non-relativistic framework, questioning whether the current and displacement current terms cancel each other out.
  • Others argue that Maxwell's equations are inherently relativistic, suggesting modifications for consistency with Galilean invariance.
  • A participant mentions three distinct situations regarding magnetic fields: currents in wires, particle beams, and moving charges, emphasizing the unique characteristics of each case.
  • Some contributions reference the Lienard-Wiechert potentials, noting their applicability for moving charges and their derivation from Maxwell's equations.
  • There is a discussion about the relationship between the Biot-Savart law and the Lienard-Wiechert solution, with participants questioning why both yield the same results under certain conditions.
  • One participant expresses confusion regarding the contribution of displacement current to the magnetic field, prompting further clarification from others.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the implications of displacement current in the context of a moving charge, nor on the significance of the results derived from different formulations of electromagnetism. Multiple competing views remain regarding the interpretation of magnetic fields in non-relativistic versus relativistic frameworks.

Contextual Notes

Limitations include the dependence on definitions of non-relativistic and relativistic frameworks, as well as unresolved questions about the contributions of displacement current to the magnetic field.

  • #31
vanhees71 said:
In the case of a uniformly moving charge you get the fields also from Lorentz boosting the Coulomb field for the charge at rest.

Per Oni said:
Sorry to be a bore about this point, but can anybody demonstrate that?

See here:

http://farside.ph.utexas.edu/teaching/em/lectures/node125.html

(two methods, take your choice)
 
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  • #32
Jtbell that paper your referring to doesn’t look like “ a Lorentz boosted coulomb field” to me. It looks a lot more complicated including a lot of maths and Greek. Oh well, someday someone will come up with something a bit more consumer friendly.
 
  • #33
I find the manuscript by Fitzpatrick excellent. It's also awailable as a textbook. I can only recommend to read his chapter on the fully relativistic treatment of electromagnetics. I never understood, why there is no textbook on classical electromagnetism that from the very beginning strictly uses the relativistic framework. Instead all authors copy more or less the classical textbooks of the first half of the 20th century (although there are excellent books among them, first of all Sommerfeld's Lectures on Theoretical Physics and Becker's book). The only exception is Landau-Lifgarbages in his vol. II, but in vol. VIII he treats the constitutive equations non-relativistic as usual. But that lamento becomes off-topic now...
 
  • #34
Per Oni said:
Jtbell that paper your referring to doesn’t look like “ a Lorentz boosted coulomb field” to me.
But that is exactly what it is.
 
  • #35
Thank you all for the comments and feedback it was most helpful and has spurred me on to do some of the maths for myself. One of my difficulties is that many textbooks "fudge" the solution by ignoring the fact that a point charge is essentially a delta distribution and they skip essential steps in the calculation. However, you all encouraged me to make the effort, after 40 years of abstinence. Thanks!
 

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