>>That's a good trick.
>
> It's not a trick, you can buy these things, they are used in research.

trick (trik)  n., adj., v. <tricked, trick-ing>
              n.
                  1.  a crafty or underhanded device, maneuver,
                       or stratagem intended to deceive or
                       cheat; artifice; ruse; wile.
                  2.  a roguish or mischievous act; practical
                       joke; prank.
                  3.  a clever or ingenious device or
                       expedient; adroit technique: the tricks
                       of the trade.
                  4.  the art or knack of doing something
                       skillfully: the trick of making others
                       laugh.

I was using the word along meaning number 3. Anything wrong with "clever or
ingenious device"? I'm sure there are more such "tricks" that one can
buy...


> With superconductors and Josephson loops you have current flowing in a
> circuit with zero resistance. There are superconducting laboratory magnets
> in common use which can do this for months. You just supply LHe. If the
> idea of current in a circuit of zero resistance bothers you [...]

It's not that it's bothering me, it's the fact that none of the proponents
of 0 resistance so far bothered to answer my question about how to in fact
measure 0 Ohm. Sorry for maybe appearing dense here, but I don't understand
a lot about superconductivity. However, I do understand a bit about
measuring and precision of measurements, and every experiment I've seen so
far had a limited precision. (Of course there is David's orang-utan
experiment, but even that is limited, in duration. And I doubt his house is
superconducting for orang-utans :)

For example at http://en.wikipedia.org/wiki/Superconductor they write that
"experiments have in fact demonstrated that currents in superconducting
rings persist for years without any measurable degradation."

Keyword here is "measurable". The /theory/ maybe says that resistance is 0
Ohms (again, I'm not a superconductor expert), but then they try to
/verify/ that theory and say (correctly) "without measurable degradation."
This would indeed indicate a /very/ low resistance, but if you take those
experiments (and not the theory they are trying to verify), you probably
will reach the conclusion that the results are that the resistance is
smaller than a finite value x -- not that the resistance is 0.

The whole discussion was about the difference between "practically 0" --
which means nothing else than "smaller than I'm able to or care to measure"
and is what we mostly deal with --, and the postulated "literally 0" --
which still needs a way to verify its existence that nobody seems to be
able to come up with. Just show me a way (a thought experiment) that
measures 0 Ohms; come up with an experiment, say what you measure, how and
with what precision (all finite, of course), and how this might lead to a
measurement of 0 Ohms. That's all I was/am asking for. Should be easy, if
it's actually as commonplace as stated.

In that superconductor current experiment I cited above, it would require
to measure the current for an infinite amount of time or with an infinitely
low resolution to be able to state 0 Ohms resistance. The moment you
introduce a limited amount of time and a limited resolution of current
measurement, you will get a result of the type "the resistance is smaller
than x" with x being > 0 Ohms.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads