1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Extended Faraday disk

  1. Mar 14, 2017 #1
    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?

  2. jcsd
  3. Mar 17, 2017 #2


    User Avatar
    Science Advisor

    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?
  4. Mar 17, 2017 #3
    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.
  5. Mar 18, 2017 #4


    User Avatar
    Science Advisor

    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.
  6. Mar 18, 2017 #5
    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?
  7. Mar 18, 2017 #6
    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.
  8. Mar 18, 2017 #7
    If torque is generated it does not oppose the applied torque.
  9. Mar 18, 2017 #8
    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.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Discussions: Extended Faraday disk
  1. Faraday cage (Replies: 10)

  2. Extended Project (Replies: 15)

  3. Faraday Cage (Replies: 1)