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My misconception?

  1. Aug 1, 2006 #1
    Sorry guys but I need someone to clear up what I consider something I may have a misconception about.

    In my understanding a magnet or magnetic forces, can do work yet expend no energy. Is this correct? And if so is there a law I probably havn't learnt yet? Is it one of those things noone can explain? Or am I wrong and there is some energy conversion, what ever it may be?

    Sorta sounds like a stupid, and possibly simple question to me at the moment. But the answer is avoiding me D:


    ~Gelsamel

    Edit: Because it seems to me that if gravity does work through potential energy conversions then either magnets are mysterious and just do things or there is some sort of magnetic potential energy.
     
    Last edited: Aug 1, 2006
  2. jcsd
  3. Aug 1, 2006 #2

    russ_watters

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    Staff: Mentor

    Magnetic potential energy works pretty much the same way as gravitational.
     
  4. Aug 1, 2006 #3
    Ah I see, so it is as simple as that. Thanks for clearing that up.
     
  5. Aug 2, 2006 #4
    That isn't quite right. For starters, magnetic potential is a vector, not scalar. Assuming we're staying out of GR, GMm/r^2 is scalar. But the main thing is that magnetic fields do no work because they only change velocity perpendicular to direction of motion: F = q v x B. F perpendicular to v always. The speed of the accelerated particle remains unchanged, only the direction is altered.
     
  6. Aug 3, 2006 #5
    Ah I see how that works, thats interesting.
     
  7. Aug 16, 2006 #6
    i thought magnetic potential is a scalar??
     
  8. Aug 16, 2006 #7

    russ_watters

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    Staff: Mentor

    According to Wik, it can either, but I'd still say that the potential energy of an object works pretty much the same in a static magnetic field as in a gravitational. I think Bo and I are talking about two different things: I'm just talking about when you pull a metalic object directly away from a magnet, you get the same d^2 relationship between distance and force and therefore the same potential energy equation. For that matter, any similar system (spring-mass, air shock) can be described via potential energy:
    http://hyperphysics.phy-astr.gsu.edu/hbase/pegrav.html
     
  9. Aug 17, 2006 #8
    I´m pretty sure that the potential is always a scalar. By definition, the Force resulting from a potential U is F = grad U, which would make no sense if U was a vector field.
     
    Last edited: Aug 17, 2006
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