I am just introduced to basics of superconductivity in Engineering Physics.(adsbygoogle = window.adsbygoogle || []).push({});

My lecturer asked a question: Is the resistance of a superconductor zero or close to zero?

And my answer was close to zero. I have read that the resistance of a superconductor is exactly zero, but then when I put some thought into it, I still feel that the resistance of a superconductor is so low that it cannot be measured, may be in the order of 10^{-30}Ω or so (or even lesser).

Reason being:

Electrons/charge carriers/cooper pairs will have a certain mass, and when they are moving, they will have some amount of kinetic energy. If we consider that there will be no collisions, and if we consider that the charge carriers move in a closed circular superconductor loop. There is a continuous change in direction (tangentially along the circular loop) There is no actual centripetal force causing the change in direction as there is NOTHING at the center of the circular loop. Hence my conclusion is work is being done continuously. Hence superconductors will be having some resistance.

One more interpretation is from Ohm's law:

I=V/R

If R is 0, V should be 0 if there is going to be some current flowing.

But Mathematically 0/0 is not defined. where as

Lim (V/R) = a finite value of I

V,R-->0

So R must be so small that it cannot be measured, and P=I^{2}R also cannot be measured. This would have given us the result that Resistance of a superconductor is 0.

If I am wrong please correct me.

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# Doubts about basics of superconductivity.

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