Moving charges and varying magnetic fields

AI Thread Summary
A steady flow of current does not induce currents in nearby conductors, but when a steady current is accelerated perpendicularly by a uniform magnetic field, it can produce a time-varying magnetic field. The discussion centers on whether charges in a conductive disk, which are accelerated, emit radiation. It is clarified that while the charges may be accelerating, if the source current remains constant over time, the magnetic field itself does not vary. However, it is acknowledged that accelerating charges can emit electromagnetic waves, leading to time-varying magnetic fields. The conversation highlights the nuances of DC and AC signals in relation to electromagnetic radiation and amplification.
Samson4
Messages
242
Reaction score
15
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?
 
Physics news on Phys.org
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?
 
  • Like
Likes Samson4
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.
 
Back
Top