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I Is there energy associated with flux pinning?

  1. Jan 15, 2017 #1
    This is probably a very naive question, but I am trying to wrap my head around the concept of flux pinning (quantum locking).

    For all intents and purposes, it appears as if a superconductor suspended above a magnetic field is defying gravity. I understand that there is no work being done (as there is no movement) but if I was to extend my arm and hold up a 100g superconductor, I would have to expend energy to prevent gravity from pulling it down. If a 100g superconductor is suspended above a magnet, is there energy associated this is 'anti-gravity' effect?

    Thanks,

    J
     
  2. jcsd
  3. Jan 15, 2017 #2

    mfb

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    Yours muscles would have to, but you would not use energy for holding it up, you would use energy for internal friction in your muscles. This is a purely biological effect. Replace your muscles by a table and you don't need energy.

    Human muscles consist of many parallel fibers that can contract. They can't do that long, however. If you keep holding your arm up, you constantly have fibers stopping contracting, while others start contracting to take over: your muscles is in constant action internally. That's where your power goes.
     
  4. Jan 15, 2017 #3
    Thanks for the answer. I guess I am still a bit confused. I agree that a table would not need any energy to hold the SC up, but there would be physical contact between the table and the SC. My muscles would have to expend energy to hold the SC above the table, or if I suspended the SC above the table from a string, I would think that some energy would be stored in the string in the form of tension. When a SC is hanging over a magnet, not in physical contact, what is the force keeping the SC from falling and hitting the surface? From your answer it appears as if the magnet and the superconductor are essentially in physical contact, but I am not clear on what is mediating this interaction between the two objects.

    What if I apply extra force (push down on) or add extra weight to the superconductor? Where does that energy go? Is it dissipated as heat? Is the amount of mass able to be levitated proportional to the strength of the magnet?

    As a side note, if it is true that there is no energy used, does this mean that if (when?) room temperature superconductors are manufactured, that levitation/suspension would essentially be free? Frictionless motion, for example a car with permanent magnets on the bottom could float along a superconducting road surface and no energy would be needed for the levitation/suspension?
     
  5. Jan 16, 2017 #4

    mfb

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    Forget the muscles. They don't help if your question is about physics. Use a table.
    What is physical contact? It is an electromagnetic force between superconductor (or any other material) and table. It is very similar to the force between superconductor and magnet, this one just has a larger range. The string is doing the same. It is all electromagnetic forces between and within materials.
    The energy to move the superconductor against a force? It is stored in the magnetic field configuration.
    With limits, but for small masses it should be.
    Right. Even today, cooling is the only thing that needs power.
     
  6. Jan 16, 2017 #5
    Thanks for taking the time to answer my question. Very helpful!
     
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