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What makes superconductors so special?

I've heard about superconductors all the time. I know they have almost zero resistance, but I was wondering what else makes them special. Please tell me any special properties superconductors have, and what causes those properties. Thank you.

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lemonie5 years ago
Like steve' said superconductors have NO resistance.
This means that you can set up an electrical-current in a circle of superconducting-"wire" and it keeps on going indefinitely* with zero voltage anywhere.
*It follows that you have a superconducting-magnet, where the field lasts indefinitely.

L

*If you interfere with the magnetic-field you can put energy in and also take it out.

Super_Nerd (author)  lemonie5 years ago
So they could be used as a high capacity battery?
They can store / release energy, so you're not really wrong there.

L
Superconductors have NO resistance, not "low", not almost zero, but NO resistance to the flow of current.

A consequence of that is that they do really interesting things with magnetic fields - take a look at quantum locked superconductors for an example. Also, a magnet will float over a superconductor.

Superconducitvity was first noted at very low, close to 0K temperatures. Modern superconductors can reach up to 80K - still cold but much easier to achieve.

Steve
No resistance is just VERY VERY low :-) correction noted! (Semantics Bah!)
The thing that makes superconductors special is their lack of electrical resistance. Duh. Right?

Their other properties, like the tendency to completely, or almost completely, exclude an external magnetic field,  are really a consequence of their lack of electrical resistance

The ability of a conductor to exclude external magnetic fields, and to levitate in the presence of an external magnetic field, is a consequence of Lenz's law, and Lenz's law is really a just statement about how electrical conductors respond to changing external magnetic fields, by producing their own internal magnetic field which repels the external one.
http://en.wikipedia.org/wiki/Lenz%27s_law
The quickest way to get a grasp on Lenz's law is to find some videos on the subject and watch what happens.  The Wiki article linked above is all equations at the top of the page, but if you scroll down, the bottom of the page links to some videos.  Or you can just search for videos on the topic of "Lenz's law" or "magnetic damping".
http://www.youtube.com/results?search_query=lenzs+law

Supposing you have a solid disc-shaped piece of conductor of some kind, e.g. a piece of copper, electric currents can circulate inside that piece of conductor, sort of the same way water moves in a glass if you stir it. 

More importantly when electric currents move in a circle, this produces magnetic field.   So a copper disc with electrical current swirling around inside it can be very strong magnet, at least temporarily.

The reason I say "temporarily" is because electrical resistance in the copper slowly damps these currents, so they don't keep swirling around indefinitely,  just like the water in  the glass will not keep swirling indefinitely, unless you keep stirring it somehow.

So it is possible levitate a conductive disk ,e.g. an aluminum one,
http://www.youtube.com/results?search_query=levitation+aluminum+disc
but you have to keep pumping energy into the system (because the "friction" of electrical resistance keeps taking it out as heat), and the external magnetic field is an AC one.

In contrast, a disk made of superconductor can levitate indefinitely in a DC magnetic field without dissipating electrical energy, that is just as long as you can keep it cold.  (For some reason superconductivity only seems to happen at relatively low temperatures.)  

That is to say the electrical current in a superconductor just keeps swirling around somehow. 

Moreover, there are other tricks that have been discovered to keep this current sort of swirling around in a direction that remains constant relative to the direction of the external field.  So you get funny effects like "magnetic locking",  e.g. a disk that sort of "sticks" in space, the same position, same orientation, relative to the external field.  You kinda have to see that one to believe it, um... here:
http://www.youtube.com/watch?v=DJV5PSpYPL0

So basically, where most of the weird, "special", properties of superconductors come from is the magnetic interactions associated with electrical currents that do not stop swirling and which are also very responsive to external magnetic fields.


gmoon5 years ago
Well, the name of course--they are just ... super!
rickharris5 years ago
Homework? Mainly their low resistance is the major property that interests people. As a result they can carry high currents without getting hot.

Unfortunately they often display this property at VERY low temperatures.

They may be made of special alloys although many materials exhibit this super conducting property.

One day perhaps they will be at the heart of the super conducting electric motor in your electric car which will never need to be recharged.

The search is for room temperature super conductors.