Moving charges and varying magnetic fields

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Discussion Overview

The discussion revolves around the behavior of moving charges in the presence of varying magnetic fields, specifically focusing on whether a steady flow of current that is accelerated can produce time-varying magnetic fields and emit radiation. Participants explore concepts related to electromagnetic radiation, the Lorentz force, and the implications for devices like amplifier tubes.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that a steady flow of current being accelerated perpendicularly by a magnetic field should emit radiation due to the acceleration of charges.
  • Others argue that if the source current is steady and not changing in time, then the magnetic field will not change in time, regardless of the acceleration of charges.
  • One participant questions the definitions of "steady" and "accelerating" in the context of current and magnetic fields.
  • There is a mention of amplifier tubes and their operation, with some participants asserting that they can produce varying fields even with a DC signal, while others challenge this by stating that amplifying a DC signal results in a DC output.
  • A later reply acknowledges that accelerating charges will emit electromagnetic waves, suggesting that time-varying magnetic fields can indeed be produced.

Areas of Agreement / Disagreement

Participants express differing views on whether a steady current that is accelerated can produce time-varying magnetic fields. Some agree that radiation can be emitted due to acceleration, while others maintain that a steady current does not lead to time variation in the magnetic field. The discussion remains unresolved with competing perspectives.

Contextual Notes

There are unresolved definitions and assumptions regarding what constitutes "steady" and "accelerating" in the context of current flow and magnetic fields. The discussion also touches on the operation of amplifier tubes, which may introduce additional complexity to the claims made.

Samson4
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I understand that a steady flow of current will not induce currents in near by conductors. But, what about a steady flow of current that is being accelerated perpendicularly by a uniform magnetic field? Wouldn't this current produce a time varying magnetic field?
dasfds.png

This is a conductive disk with axial current flow.
As the current is curved to the right, shouldn't it emit radiation in the direction of the blue lines?
 
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Nobody has answered yet here, so I'll just give my best guess of saying: yes, I agree, these charges are being accelerated, and thus should emit radiation.

Do you have reason to believe it is not the case?
 
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rumborak said:
Nobody has answered yet here, so I'll just give my best guess of saying: yes, I agree, these charges are being accelerated, and thus should emit radiation.

Do you have reason to believe it is not the case?

Well because radiation can only be varying. So; if it does emit radiation, it would mean dc to ac conversions could be done with just a copper disk and a magnet.
 
What do you mean by "steady" and "accelerating"? If it's a steady current, then there's no time variation in the magnetic field.
 
A steady flow of current, dc, that is being accelerated perpendicular to the electric field by a magnetic field. The current is uninterupted but it must be accelerated as it curves by definition of the lorentz force. Does it produce a varying magnetic field?
 
The charges that make up the current can be accelerating, but if the source current is not changing in time, then the magnetic field won't change in time.
 
Khashishi said:
The charges that make up the current can be accelerating, but if the source current is not changing in time, then the magnetic field won't change in time.

Why does it behave differently that a flow of electrons in a vacuum? For example, amplifier tubes use dc and accelerating electrons to produce varying fields.
 
What kind of amplifier tubes are you talking about? If you amplify a DC signal, you get a DC signal.
 
Khashishi said:
What kind of amplifier tubes are you talking about? If you amplify a DC signal, you get a DC signal.
Any tube amp uses ac to modulate dc. A magnetron uses the lorentz acceleration of a static magnetic field to produce em waves. A krlystron uses magnetic fields to modulate dc.
 
  • #10
Sorry, I got confused. True, accelerating charges will emit EM waves, regardless of if the current is changing. So, you can get time-varying magnetic fields.
 

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