Super-conductors

[5614]

a super-conductor is a wire [electronics] which has 0-ohm resistance.

 

right here is what happened [includes background info] there is a problem somewhere, but i dont know what it is.... can someone please point it out!?!

 

i thought superconductors were possible, they occured when a wire was at absolute zero or very high [dont know how high!]...

 

according to my friends science teacher, with enough current and/or voltage, ALL wires will melt, due to the resistance...

 

i said, "no" not in superconductors!

whos wrong.?.?.?

[JaKiri]

Superconductors do exist, but all school science is simplified, so the teacher was knowingly lying (as the do, and are forced to do, all the time)

[swansont]

There is a point where superconductors fail, as well. You cannot put an unlimited current through them.

[5614]

There is a point where superconductors fail, as well. You cannot put an unlimited current through them.

 

that answers my question swansont, but are you sure, with no resistance, why would there be any heat loss, and if there is no heat then why would th wire melt?

[atinymonkey]

They only have 0-ohm with a set current, exceed the current and the resistance increases. They ain't magic.

[5614]

are you sure? is this theoretical? at what kind of current will this happen? are you talking something realistic or a few million A

[YT2095]

a super conductor of a fixed diameter will still only allow so many electrons to flow at a time and at the same speed, therfore there is a top limit

[5614]

yeah i spose, but any idea what the limit is?

[YT2095]

non at all to be honest, I would imagine it would be a variation on a Rho calculation, but I`ve had little experience in the feild of super conductors and couldn`t say with any certainty.

[JaKiri]

yeah i spose, but any idea what the limit is?

 

It depends entirely on the superconductor. They're not identical.

[qazibasit]

well actually super conductors work at the poles so no heat loss and unlimited current can pass through it but as everything has a limit it also reaches its maximum limit.

[[Tycho?]]

Is it true that superconductors are always the same temperature throughout? I read this in a sci-fi book, but it seems a rather odd property.

[swansont]

This is just based on what I remember from the group up the hall from me in school, but in superconductors, the magnetic field lines are trapped by the material (flux pinning sites). Above a certain current density (critical current), the flux lines start moving and exert forces on the electrons that destroy the superconductivity. The value depends on the superconductor.

 

 

 

More on the critical current

 

 

more stuff

 

The cartoon I drew using the jargon I learned from that group.

[5614]

do hot superconductors work in a similar way to cold superconductors???

 

in that cold ones have cooper pairs, do hot superconductors also form cooper pairs?

 

all ive found so far on the matter is:

In 1986, "high-temperature superconductivity[/url']" was discovered (i.e. superconductivity at temperatures considerably above the previous limit of about 30 K; up to about 130 K). It is believed that at these temperatures other effects are at play; these effects are not yet fully understood. (It is possible that these unknown effects also control superconductivity even at low temperatures for some materials)

which isnt much help!

[bloodhound]

a super conductor of a fixed diameter will still only allow so many electrons to flow at a time and at the same speed, therfore there is a top limit

therefore if u take the speed of light to be the limit of the electron speed. you should get that top limit where the superconductor of the given diameter fails

[swansont]

therefore if u take the speed of light to be the limit of the electron speed. you should get that top limit where the superconductor of the given diameter fails

 

Actual electrons don't flow anywhere near the speed of light in conductors (super or otherwise). The speed of the current flow and the speed of electron flow are not the same thing.

[bloodhound]

Actual electrons don't flow anywhere near the speed of light in conductors (super or otherwise). The speed of the current flow and the speed of electron flow are not the same thing.

ok ok. i am not a physistict. can you explain whats the difference between current flow and the electron flow is

[5614]

and how 'hot' super-conductors work?

 

thanks

[swansont]

ok ok. i am not a physistict. can you explain whats the difference between current flow and the electron flow is

 

Consider a train. When the engine starts moving, it pulls/pushes all of the cars along. For electrons, the push goes at the speed of light - when an electron at one end of the train moves, the one at the other end feels it at a time c/L later. But the train itself moves very slow.

 

But current is the number of electrons moving past a point per unit time. The key here is that there is more than one track - copper atoms, for example, are spaced only a couple of Angstroms apart, and each can potentially contribute a conduction electron to current flow. Here's a quick estimate: a 1 mm thick wire is several million atoms across, or 10¹² or so atoms in area, giving 10²¹ atoms per meter. An amp is 6.25 x 10¹⁸ electrons per second, so these 10²¹ electrons only have to move 6.25 mm/sec to give you that current.

 

(The thermal speed of the electrons at room temperature is much higher than that, but that's random and doesn't contribute to net current flow)

[Guest Sev]

Yes, I believe both super-cooled and "hot" superconductors (or "not-so-cold" more accurately) form cooper pairs. However, there are also certain types of superconductor which do not, regardless of what their superconductance temperature range is.

 

However, I'm not an expert in the field, but that is what I've been lead to believe through talking to people who are.

 

Oh, and yes superconductors are the exact same temperature throughout.