Extended Faraday Disk: How is Energy Conserved?

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Discussion Overview

The discussion revolves around the mechanics of an extended Faraday disk system, particularly focusing on energy conservation, current generation, and the effects of magnetic fields and forces within the setup. Participants explore theoretical implications and practical configurations related to the operation of the disk, including the role of magnetic circuits and the behavior of currents in conductive materials.

Discussion Character

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

Main Points Raised

  • One participant describes a configuration with two opposing magnets within a copper cylinder, generating current and torque, and questions how energy is conserved in this system.
  • Another participant points out the lack of a closed path for the electron current circuit, suggesting that a voltage may be generated without current flow and questions the magnet polarity.
  • A similar concern about the current circuit is reiterated, emphasizing the need for brushes to complete the circuit, while also noting the complexity of the diagram.
  • There is a discussion about whether axial currents would cancel out due to the symmetrical nature of the magnetic field and copper cylinder, raising questions about the conditions under which current would flow.
  • One participant introduces the concept of a counter torque acting on the electrons due to Lorentz force and speculates on the role of resistance in transmitting this force throughout the disk, also questioning the behavior of the disk if it were superconducting.
  • Another participant echoes the concern about axial currents canceling and expresses uncertainty about the implications of the previous statements.
  • A question is posed regarding the path electrons would take in the system, considering all blocks are made of the same conductive material and connected to a DC power source.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the operation of the Faraday disk, the nature of current flow, and the implications of magnetic fields. The discussion remains unresolved, with no consensus on the mechanisms at play or the conditions necessary for energy conservation.

Contextual Notes

Participants highlight limitations in the current understanding of the magnetic circuit and electron flow, including assumptions about symmetry and the need for additional components like brushes. The discussion also reflects uncertainty regarding the effects of superconductivity on the system.

Samson4
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In the diagram, I am focusing on the area in the green circle.
So this is basically 2 Faraday disk with the magnets opposing and concealed in a copper cylinder. Now if we spin the cylinder a current is generated such as the current following the red arrows.

My Confusion: As the current passes between the magnets, a torque is also produced. The force should be in the same direction as the torque that created the current. Seeing as how most of the lines of flux coming from the north face of the magnets are parallel to the cylinder walls and perpendicular to the disks; shouldn't there be a current generated and a torque. How is energy conserved?

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You have closed the “purple” magnetic circuit, but not the “red” electron current circuit.
I can see no path for the current to close the loop, so a voltage will be generated without current.
Are you sure you have the correct magnet polarity?
 
Baluncore said:
You have closed the “purple” magnetic circuit, but not the “red” electron current circuit.
I can see no path for the current to close the loop, so a voltage will be generated without current.
Are you sure you have the correct magnet polarity?

It would have brushes just like a regular faraday disk. I didn't want to add anymore junk to such a mess of color. A brush would be present on the rods on both sides of the cylinder.
 
Any purple flux that passes through a copper disk must also pass back through the copper cylinder.
Will all axial currents not cancel to zero?
The copper is never subjected to a changing magnetic flux since the field and copper are axially symmetrical.
 
There is a counter torque, because the electrons that form the current feel a Lorentz force, and then somehow that force is transmitted to the whole disk. Maybe the force is transmitted by resistance. Does Faraday disk work if the disk is superconducting?
 
Baluncore said:
Any purple flux that passes through a copper disk must also pass back through the copper cylinder.
Will all axial currents not cancel to zero?
The copper is never subjected to a changing magnetic flux since the field and copper are axially symmetrical.

So far that's the only solution I can think of. So there should be no current flow from 1 rod to the other.
I don't understand what you mean with the second part of your post.
 
jartsa said:
There is a counter torque, because the electrons that form the current feel a Lorentz force, and then somehow that force is transmitted to the whole disk. Maybe the force is transmitted by resistance. Does Faraday disk work if the disk is superconducting?

If torque is generated it does not oppose the applied torque.
 
On a related note, which path do you think the electrons will follow in this image? All the blocks are the same conductive material. The black circles are connections at a dc power source.
path.png
 

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