How does a superconductivity cable achieve zero resistance?

[StephenP91]

Well. I have the image of the question.

http://img99.imageshack.us/img99/6834/question5.png

Question b)ii).

I know that the total resistance of the cable is 0 even though the copper itself still has resistance. I just want to know how the combination of the Superconducting filaments combined with the copper itself makes the over all resistance 0.

Thank you,
Stephen.

 

[mgb_phys]

Think of it has the electircity taking the easiest path.
If you have two resistors in parallel and one has twice the resistance of the other, then twice as much electricty will flow down the small resistance (the easiest path) as down the high resistance path.

With a superconductor, one of the paths is perfectly 'easy' so infinitely more times as much electricty will flow down this path as the copper.
Or looking at it the other way - none of the electricty will take the copper path and the overall conductivity is still zero.

 

[StephenP91]

I think I understand now. Because I is inversely proportional to R and because the filament's R is infinitely smaller than the copper's R, the filament gets infinitely more/all of the current.

Well that's how I've made sense of it. Whether it's right or not, I don't know.