>> I really don't see the problem.  Do you understand what happens if you 
>> short a battery with a wire?  You will get a huge current flowing even 
>> though the voltage across the wire is virtually zero.
>
> How the hell do you figure that?

Because the resistance of the wire is way lower than the internal resistance 
of the battery.  DId you never notice that the more current you draw from a 
battery the lower the voltage across its terminals?  If you *short* a 
battery, the voltage is pretty much zero.

>> If you put a super-conductor across the terminals of a battery, would you 
>> expect a current to still flow? After all, the voltage across the 
>> superconductor would be zero...
>
> Where would you measure the difference? You need two points.

The two terminals of the battery.  Connect a super-conductor between the two 
terminals of a 9V battery and put your volt-meter across the battery 
terminals. It *will* be zero volts.

> Anyway, presumably a superconducting magnet is bizare enough that Ohm's 
> law doesn't apply. (Hmm, I = V/R where R = 0. Yeah, that looks pretty 
> undefined to... oh, wait, you're that guy who things that division by zero 
> is defined, aren't you?)

You don't need to do that, batteries have an internal resistance, Ri, so the 
current flowing will simply be Vbattery / Rinternal.  With zero volts across 
the super-conductor, but a current flowing.

Ohms law works perfectly well, the fact that R is zero simply means you can 
have whatever current flowing you want with no potential difference.  Which 
is exactly how superconductors work.

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