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Thread: Superconductor Question

  1. #1 Superconductor Question 
    Forum Bachelors Degree Waveman28's Avatar
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    We know that superconductors generate a powerful magnetic field when carrying a current. We also know that they expel all external magnetic fields, which is called the Meisner effect, which will cause a superconductor to levitate if placed over a magnet. However, we also know from classical physics that 2 parallel current carrying conductors will experience a force (the Lorentz force). If both currents are going in the same direction, an attraction effect will result, and if they are going in opposite directions, they will repel. I do know that superconductors have a critical current density limit, which when passed will no longer result in its superconductivity.

    So, my question is: If we have 2 parallel current carrying superconductor wires who's currents are travelling in the same direction, will they attract each other? If so, this would seem to go against the Meisner effect.


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  3. #2 Re: Superconductor Question 
    Time Lord
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    Quote Originally Posted by Waveman28
    We know that superconductors generate a powerful magnetic field when carrying a current. We also know that they expel all external magnetic fields, which is called the Meisner effect, which will cause a superconductor to levitate if placed over a magnet. However, we also know from classical physics that 2 parallel current carrying conductors will experience a force (the Lorentz force). If both currents are going in the same direction, an attraction effect will result, and if they are going in opposite directions, they will repel. I do know that superconductors have a critical current density limit, which when passed will no longer result in its superconductivity.

    So, my question is: If we have 2 parallel current carrying superconductor wires who's currents are travelling in the same direction, will they attract each other? If so, this would seem to go against the Meisner effect.
    Maybe electric fields generated by other superconductors are a special exception to the rule? This is a really interesting effect. I had never heard of it before you brought it up.

    http://en.wikipedia.org/wiki/Meissner_effect

    Going off this article, it seems that effect is caused by currents in the wire rapidly readjusting to compensate for the external magnetic field? Do I understand that right? If the object creating the field were another superconductor, then it stands to reason that it would be able to continually compensate for the other's compensations.


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  4. #3  
    Forum Bachelors Degree Waveman28's Avatar
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    Yes it is an interesting effect, I believe it also has many powerful practical applications as well.

    Your interpretation of how superconductivity works is correct. When an external magnetic field comes into contact with a superconductor, it generates an electric current in the superconductor, which in turn generates a magnetic field which equal in strength to the original magnetic field, thus cancelling it out.

    However, placing two superconductors next to each other seems to makes things a bit more tricky, as both are going to try to cancel each others fields......

    Where is Dr. Rocket when you need him?
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