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Resistance at absolute zero

  1. Jul 23, 2012 #1
    I was wondering, since resistance decreases along with temperature for most metallic conductors (usually power function), in theory, if this conductor were to be at zero kelvin, would the resistance of this material also be precisely zero, or would it just be some extremely small value?
    If it was zero ohms, then short circuiting an ideal voltage source with a wire in these conditions would create an infinite current, which i believe is physically impossible, and so we have yet another reason why absolute zero isn't achievable. However it doesn't rule it out theoretically.
    Anyway, does anyone have any ideas on the matter?
     
  2. jcsd
  3. Jul 23, 2012 #2

    phinds

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    Nothing gets to absolute zero, but when you get really close, it's my understanding that the resistance goes to zero because the mechanism that causes resistance goes away.

    As for an idea power supply, there is no such thing so your statement is not meaningful.
     
  4. Jul 23, 2012 #3
    I know those things are not possible, I was just speculating. There's no need to get heated.
    Anyways thanks for replying. I took a little time to look more extensively and i found the following:
    But maybe you're right. What particular mechanism did you have in mind?
     
  5. Jul 23, 2012 #4
    It is wrong to think that you will have an infinite current.
    The wire could well have zero resistance (this is what superconductors are) but the wire will also have an inductance which (as far as I know) is not temperature dependant. The inductance determines the rate at which current will rise so the best you can say is that a wire with resistance = 0 but inductance = 10H (for the sake of argument) will be observed to have a current increasing at 1A/s when connected to
    10V (e = Ldi/dt)
     
  6. Jul 23, 2012 #5
  7. Jul 23, 2012 #6

    phinds

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    Yes, that's correct. I SHOULD have said superconductors, not just any material.

    To my considerably surprize, when I looked at superconductors briefly last year, I found that two of the best conductors I am aware of, copper and gold, are NOT superconductors near zero degrees.
     
  8. Jul 24, 2012 #7
    I asked an ECE phd student I recently met about this, and he told me that it would only impede the current from reaching an infinite amount if it were alternating. Probably though, for direct current, capacitance (I guess normal wires have tiny capacitance just as inductance?) would kick in having the same effect.

    Ok, thank you for the replies, you've all been very helpful.
     
  9. Jul 24, 2012 #8

    phinds

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    Anyway, you can't SUPPLY infinite current, so whether or not it has that capacity is irrelevant from a practical point of view.
     
  10. Jul 24, 2012 #9
    What would be the drift speed of this so called infinite current?
     
  11. Jul 24, 2012 #10

    phinds

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    Anything you want it to be.

    The statement

    "If the current is infinite, the drift speed is X"

    Is an absolutely true statement regardless of what X is because a false premise implies any result you like.
     
  12. Jul 25, 2012 #11
    You haven't heard of silver? :P
     
  13. Jul 25, 2012 #12

    mfb

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    Superconductors have a maximal current density - try to enforce more current, and they will stop to be superconducting. The resistance heats the superconductor, it can carry even less current, and heats more, and you get a nice quench.

    While the current is not infinite, it can stay circulating for (nearly) an infinite time in a superconducting circuit.
     
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