An interest thought experiment

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Discussion Overview

The discussion revolves around a thought experiment involving a detector that can sense electromagnetic waves while a person (A) runs at a constant velocity relative to a charged particle. Participants explore whether the detector would flash under these conditions, considering the nature of the electromagnetic fields and the definition of the detector's capabilities.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant suggests that the detector will flash because the electric and magnetic fields in A's frame are not static, referencing Classical Electrodynamics by Jackson.
  • Another participant questions the assumption that the detector would detect an electromagnetic wave, arguing that A would only detect a magnetic field due to the moving charge being perceived as an electric current.
  • Another participant emphasizes that the electric and magnetic fields are changing continuously, indicating a dynamic situation rather than a static one.
  • There is a discussion about the definition of the detector, with one participant stating that if the detector responds to any time-varying fields, it would trigger, but if it only responds to fields with a specific wave form, it would not.

Areas of Agreement / Disagreement

Participants express differing views on whether the detector would flash, with some arguing it would due to changing fields, while others contend that the lack of a wave form in the fields means it would not. The discussion remains unresolved regarding the detector's capabilities and the nature of the fields involved.

Contextual Notes

There is ambiguity regarding the definition of the detector and what constitutes an electromagnetic wave. The discussion also highlights the dependence on the interpretation of the fields' characteristics and the conditions under which the detector operates.

qinglong.1397
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Suppose we have a detector which can detect the electromagnetic wave. If there exists the electromagnetic wave, the detector will flash.

Now, A holds this detector and runs at a constant velocity relative to a charged particle. Will the detector flash? I think it will. In Chapter 11.10 of Classical Electrodynamics by Jackson, we already calculate the electric and magnetic fields in A's frame. The fields are not static. So I think the detector should flash. But the problem is that the fields do not have the wave form. There is no phase term in the mathematical expressions. So, what is the problem?
 
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qinglong.1397 said:
Suppose we have a detector which can detect the electromagnetic wave. If there exists the electromagnetic wave, the detector will flash.

Now, A holds this detector and runs at a constant velocity relative to a charged particle. Will the detector flash? I think it will. In Chapter 11.10 of Classical Electrodynamics by Jackson, we already calculate the electric and magnetic fields in A's frame. The fields are not static. So I think the detector should flash. But the problem is that the fields do not have the wave form. There is no phase term in the mathematical expressions. So, what is the problem?
A would detect a magnetic field since he will view the (relatively) moving charge as an electric current. This would simply be an application of Ampere's law. He would also be able to detect an induced current if he was carrying a conducting loop connected to a galvanometer. Why do you think he would detect an electromagnetic wave from A?

AM
 
That is because the electric and magnetic fields are both changing all the time. This is neither a static electric problem nor a static magnetic problem.
 
qinglong.1397 said:
So, what is the problem?
The problem is simply a poor description of the detector. What does it detect? If just any time varying fields then yes, it triggers. If it only detects fields with "the wave form" then it will not trigger.
 
DaleSpam said:
The problem is simply a poor description of the detector. What does it detect? If just any time varying fields then yes, it triggers. If it only detects fields with "the wave form" then it will not trigger.

Oh, yeah. Thanks for your reply. I think I should give a clear definition of the detector. Sorry about that.
 

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