Are there reactance effects for high frequency DC?

[Mechatrommer]

in physical reality, you can make V and R on the macro/larger/external system scale, current will follow afterward. in effect the internal nodes potential however will vary in time based on each component's reactance (ie the current flow through it, with some right combination, they will oscilate. and then dampen if not agitated by another current flow. the hardest part is try to understand the balance of them (the internal nodes), thats what ee school is for. btw dc is whenever there is nonzero net of electrons transfer at a particular time and space reference, so if you pick less than a period of a freq as your time reference, then you'll have a dc component in pure ac signal, my 2cnts.

[Brumby]

nope: no voltage no current. you cant make up current source if you dont have potential (charge) difference available between 2 space connected by a transfer medium. btw, ac is whenever the electrons' net momentum change. and they always follow the rules because they dont have a choice, not like human.

Yeah this is something I've always not been too happy about, whenever the focus is on current. I've even read an author who said that BECAUSE of current flow through a resistor, it CREATES a voltage. Now, in all fairness, the resistor is sitting in the circuit, and the actual potential difference is being caused by a voltage source.

(Since I'm the OP I think we should allow a small side discussion on this, as it's related to my original question and I want to know what is real situation with this current v voltage thing).

Sometimes trying to discuss relationships can be best served by looking at a extreme and/or limiting case...

In the case of voltage and current - what can be said when there is a current through a superconductor?

[R005T3r]

Superconductors...They advertise the material has 0 DC resistance, but in reality it's not like that: even if it's infinitesimal to a certain degree of magnitude does not mean it's actually zero: it approaches to zero, but it's not zero!. So, what's the deal about superconductors? It's that they dissipate so low power that it will make the difference in a mains distribution system, as a result if anyone uses it we will have an efficiency boost of the 30% on the actual global distribution system (and it's a huge amount)

However, the "ideal" wire such as the ones you see on the simulator, it will never-ever exist. As for current, if you will have 1A flowing trough your superconductor, it will be: 1.6x10^19 electrons per second again, you can say current flowing trough an object, but as a regard of the voltage drop? it would be near to zero but there will be some value... This means that the definition is well formulated.

[T3sl4co1l]

Superconductors...They advertise the material has 0 impeadence

No, superconductors have zero DC resistance.

Period, end of story.

No one has ever said they have zero impedance, except erroneously!

Indeed, type 2 superconductors have AC resistance -- it's even macroscopically visible!

Type 1 superconductors, carefully prepared, have quite low AC losses, even at high frequencies: resonators, of polished niobium at 2.2K, have a Q factor higher than most quartz crystals -- about 3 million.

The loss is small but nonetheless present, and it's poorly understood.  One could only guess at the mechanisms; surface quality and purity probably have a lot to do with it.

All superconductors cease at some finite frequency, because that is the frequency characteristic of the binding energy of the Cooper pairs, ~1meV, which is in the 10s of GHz microwave region.

This can be used as a very fast switch, actually: the superconducting electrons are a thermal reservoir somewhat separate from the material itself (giving rise to the electronic heat capacity -- usually a small fraction of the total heat capacity, which is predominantly due to phonons -- acoustic vibrations).  If the electrons are heated by zapping them with microwaves or higher frequencies, superconduction stops instantly, then eventually recovers as the electrons come back to equilibrium.

Tim

[R005T3r]

Yes, I wanted to mean DC resistance, not impedance... My bad.

[Zero999]

All superconductors cease at some finite frequency, because that is the frequency characteristic of the binding energy of the Cooper pairs, ~1meV, which is in the 10s of GHz microwave region.

This can be used as a very fast switch, actually: the superconducting electrons are a thermal reservoir somewhat separate from the material itself (giving rise to the electronic heat capacity -- usually a small fraction of the total heat capacity, which is predominantly due to phonons -- acoustic vibrations).  If the electrons are heated by zapping them with microwaves or higher frequencies, superconduction stops instantly, then eventually recovers as the electrons come back to equilibrium.

I take it that means a superconductor stops superconducting when exposed to photons with a high enough energy to break the Cooper pairs? So if a superconducting magnet were exposed to visible radiation it would lose some of its magnetic field.

[T3sl4co1l]

Yes; of course, this only applies to the penetration depth of light in the material -- perhaps 100s of nm.

It's of practical use (I think?) in superconducting thin films, but in a bulk material, there's plenty of sub-surface left to handle things; and for that matter, in a practical superconducting cable, there's a jacket of copper metal around everything, which is even less transparent.

If the current has a place to go, the magnetic field magnitude won't change.

Tim