Qv x B force in electron's proper frame

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Discussion Overview

The discussion revolves around explaining the magnetic force experienced by an electron in its own reference frame, specifically the term B x v, without relying on advanced concepts such as relativistic invariants, 4-vectors, or tensors. The participants aim to communicate these ideas to an audience familiar with non-relativistic electromagnetics and Maxwell's equations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the B x v force can be explained in the electron's frame without advanced concepts, targeting an audience familiar with non-relativistic electromagnetics.
  • Another participant presents the Lorentz force equation, noting that in the electron's frame, the term B x v disappears, leaving only the electric field, which they argue does not help resolve the Faraday paradox due to the need for transforming magnetic fields and considering the frame's rotation.
  • Some participants assert that Maxwell's equations inherently describe a relativistic field theory, suggesting that the notion of non-relativistic electromagnetics is inconsistent with the fundamental principles of these equations.
  • A participant reflects on their educational experience, indicating that while they learned to apply Maxwell's equations in a single reference frame, they did not consider transformations to other frames, implying a limitation in understanding the implications of moving charges or wires in magnetic fields.
  • Several participants agree that in the electron's rest frame, the velocity is zero, leading to the conclusion that B x v equals zero, regardless of the magnetic field.
  • One participant shares a personal anecdote about a common misconception regarding the distance a muon travels in its rest frame, highlighting a broader issue of understanding in the context of relativistic effects.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of non-relativistic electromagnetics and the interpretation of Maxwell's equations. While some agree on the outcome that B x v equals zero in the electron's rest frame, there is no consensus on the broader implications or the educational approach to these concepts.

Contextual Notes

Participants note limitations in their understanding of how to transform field properties between reference frames, particularly in the context of moving charges and wires. There is also an acknowledgment of the complexities involved in explaining these concepts without advanced theoretical frameworks.

Swamp Thing
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Can we describe / explain the B x v force in the electron's own reference frame without reference to relativistic invariants, 4-vectors, tensors et al?

The aim would be to explain things like the following video without the notion of "field lines" that electrons and wires move through. But the target audience would be people who understand non-relativistic electromagnetics including Maxwell's equations.

 
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The Lorenz force
$$\mathbf F = q(\mathbf E +\mathbf v \times \mathbf B)$$
for a particle (charge ##q##) in an electric field ##\mathbf E## and magnetic field ##\mathbf B##, looks like
$$F'=q\mathbf E'$$
in the particle's frame. Where ##\mathbf E'## is the electric field in the particle frame.

This means that in the particle's perspective, there is no ##\mathbf v \times\mathbf B## term, only electric fields (as its own velocity is null in that frame).

Edit: I do not think this helps much to solve the Faraday paradox. As (1) you also have to transform the magnetic fields (2) the frame is rotating (3) it is a metal with currents not a single electron.
 
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Swamp Thing said:
people who understand non-relativistic electromagnetics including Maxwell's equations
There is no such thing. Maxwell’s equations describe a relativistic field theory by construction. In fact, it is the field theory that led Einstein to develop relativity because it was not consistent with non-relativistic physics.
 
Orodruin said:
There is no such thing. Maxwell’s equations describe a relativistic field theory by construction. In fact, it is the field theory that led Einstein to develop relativity because it was not consistent with non-relativistic physics.

In our EE course (late 1970s) we learnt Maxwell's equations and how to apply them in a single reference frame, but not how to transform the field properties to other frames. When dealing with charges or wires in a magnetic field we would do the sums in the magnets reference frame. I don't remember thinking about how it would look in the electron or wire frame.

So from the replies, it seems that that kind of target audience is stuck with moving lines of force cutting a stationary wire or moving charge (naive pseudo relativistic intuition) ?
 
Swamp Thing said:
Can we describe / explain the B x v force in the electron's own reference frame without reference to relativistic invariants, 4-vectors, tensors et al?
Sure. ##v=0## so ##B \times v=0## regardless of ##B##
 
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Beat me to it!
 
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Dale said:
Sure. ##v=0## so ##B \times v=0## regardless of ##B##
This reminds me of that time I discovered the question "How far does the muon travel in its rest frame?" in a modern physics course with the correction template unironically suggesting something different from zero ...

It is now a favourite question of mine to pose to students (obviously with the correct answer) as it illustrates a key concept that way too many just don't grasp ...
 
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