Not sure what you mean, or how to reply. The voltage potential must be created somehow. In a home, that might be from energy conversion at the power company, or energy conversion in a solar panel. Electrons were moved in both cases.
Or liken it to a capacitor charging. There's no current flow from end to end, but electrons are drawn to or away from the plates.
Compare voltage (moving electrons to create a charge imbalance) with lifting a bucket of water overhead.
Inserting a conductor and load in the former, or pipe and water wheel to the latter, will convert the potential energy in each into work done. The electrons will flow, the water will flow, until the systems are again balanced.
That's one for the physicists. I suppose the atoms in the superconductor are at such an idle state that the electrons can move uninhibited.
To get current without voltage, you need a superconductor.
To get voltage without current you need a perfect insulator.
Both are possible.
The current problem for science (no pun intended) is that maintaining the superconductivity requires a power source.
godfrey, I admire your succinctness.
Last edited:
Yes found some info I posted it in post #20
Its got a wow factor...😀
Thank's for the input..🙂..it might seem stupid but its still interesting..
Regards
M. Gregg
Its got a wow factor...😀
Thank's for the input..🙂..it might seem stupid but its still interesting..
Regards
M. Gregg
Last edited:
Energy..
WIKI again..
Quote..we have no knowledge what energy is.
Energy - Wikipedia, the free encyclopedia
Regards
M. Gregg
WIKI again..
Quote..we have no knowledge what energy is.
Energy - Wikipedia, the free encyclopedia
Regards
M. Gregg
And surely, Ohm's Law is just a description of the relationship between three parameters - voltage, current and resistance are just three ways of viewing and describing a single phenomenon - the way electrons behave in a conductor. They are not entities in themselves. There is a fundamental difference between scientific description and scientific explanation. Explanation is a difficult and evasive concept. Newton's laws were probably originally seen as explanation, but as deeper structures of matter were revealed, it became clear that they were just descriptions, and that explanation had to be sought at a deeper level. That "deeper level" is always shifting as we learn more.
Last edited:
Ohm's Law and Newton's laws should not be compared. Ohm's Law is an approximation which happens to be true for many conductors - it is not a universal physical law.
Newton's laws of motion are universal laws which apply to any stuff in any situation where the classical mechanics approximations are valid: so not very small (quantum) and not very big (general relativity).
To answer the OP's original question: electrical resistance is caused by electron scattering. It can be shown that, given certain assumptions, the ratio between current and voltage will be constant. These assumptions happen to be more or less true for many conductors so many conductors are ohmic.
Superconductors work by eliminating the scattering. For low temperature superconductors this is due to the formation of Cooper pairs. For high temperature superconductors something similar must be happening but there is not yet a clear theory.
The energy produced by current in a resistance is simply energy conversion from potential energy to heat. Energy is the ability to do work. Energy conservation comes from the fact that the laws of physics are invariant under time translation (Noether's theorem?).
I guess all this could be found by Googling. Alternatively, do an undergraduate degree in physics. Most of this stuff is covered in the first or second year. A rough approximation to it may be found in school physics too (A-level in the UK).
Newton's laws of motion are universal laws which apply to any stuff in any situation where the classical mechanics approximations are valid: so not very small (quantum) and not very big (general relativity).
To answer the OP's original question: electrical resistance is caused by electron scattering. It can be shown that, given certain assumptions, the ratio between current and voltage will be constant. These assumptions happen to be more or less true for many conductors so many conductors are ohmic.
Superconductors work by eliminating the scattering. For low temperature superconductors this is due to the formation of Cooper pairs. For high temperature superconductors something similar must be happening but there is not yet a clear theory.
The energy produced by current in a resistance is simply energy conversion from potential energy to heat. Energy is the ability to do work. Energy conservation comes from the fact that the laws of physics are invariant under time translation (Noether's theorem?).
I guess all this could be found by Googling. Alternatively, do an undergraduate degree in physics. Most of this stuff is covered in the first or second year. A rough approximation to it may be found in school physics too (A-level in the UK).
DF96,
How is the energy carried is this back to the Feynman diagrams again?
(Transfer of energy)
Regards
M. Gregg
How is the energy carried is this back to the Feynman diagrams again?
(Transfer of energy)
Regards
M. Gregg
Last edited:
I'm not certain I understand the question. The electrons have potential energy. They lose this energy in collisions and it becomes heat. Haven't we already said this?
I'm thinking along these lines..
Feynman Diagrams and Forces Between Particles
Or am I on the wrong track?
Regards
M. Gregg
Feynman Diagrams and Forces Between Particles
Or am I on the wrong track?
Regards
M. Gregg
If you understand Feynman diagrams then I don't know why you asked the original question.
If you don't understand Feynman diagrams then they can't help you.
Find a good physics textbook at the appropriate level for you (i.e. you can just about understand the first chapter). Read it. Come back with your questions. We can't provide the content of four years of study in a thread. It might help us if you say what your level in physics is.
If you don't understand Feynman diagrams then they can't help you.
Find a good physics textbook at the appropriate level for you (i.e. you can just about understand the first chapter). Read it. Come back with your questions. We can't provide the content of four years of study in a thread. It might help us if you say what your level in physics is.
Cooper pairs... never heard of it.🙂 Like charges being attracted to each other? Heady stuff. It's among the things that make this science so interesting, these twists and turns from what is considered normal.
The wiki states that, "The energy of the pairing interaction is quite weak, of the order of 10−3eV," which is sort of counter-intuitive because it would seem that some greater amount of energy would be stored in getting them together. It must be dependent on the "electron–phonon interactions," which I'm also clueless about.
Reminds me of a Bob Pease interview I read the other day. When his physics courses at MIT got to be, umm, a little too "out there," he became disillusioned and less interested so instead focused on an electronics program.
The wiki states that, "The energy of the pairing interaction is quite weak, of the order of 10−3eV," which is sort of counter-intuitive because it would seem that some greater amount of energy would be stored in getting them together. It must be dependent on the "electron–phonon interactions," which I'm also clueless about.
Reminds me of a Bob Pease interview I read the other day. When his physics courses at MIT got to be, umm, a little too "out there," he became disillusioned and less interested so instead focused on an electronics program.
Actually 'voltage drop' is not a good term in this context. You need a voltage difference across an element to make a current flow. The voltage difference provides an excess of electrons on one side of the element, and they flow from the excess to the other node, and that's the current. How much current does flow from a particular voltage difference? That depends on, quite literally, the resistance.
You said before, voltage drop isn't on one side. Correct. A voltage difference can only exists BETWEEN two points: the voltage difference or potential difference. We are used to talk about voltage but that is really not correct, we should always talk about a voltage difference. But because we most often implicitly refer to a voltage difference between a node and ground, we can get away with the sloppy language and still understand each other.
jan
Actually, to get the current you have to use voltage. The rate of change of the current will be dependent on the inductance of the system and the voltage placed across it.
More nitpicking: you have to keep thermal energy away from the conductors.
But yah, that requires a monster fridge.
jn
jneutron,
So whats the difference in the type of flow in the standard conductor and super conductor..is there any change in "Type" of flow dependant on voltage..ie skin effect or other?
Regards
M. Gregg
So whats the difference in the type of flow in the standard conductor and super conductor..is there any change in "Type" of flow dependant on voltage..ie skin effect or other?
Regards
M. Gregg
I can't let this go uncommented. Therefore, I'll try to find a short, one-sentence-answer for each of the statements in your post. I do not guarantee a readable length of these sentences, however 😀
Careful! No electron is ever 'converted' - there are laws of conservation at work: Electrons move around, aquire energy and lose energy, but they're still electrons, unless you hit them with a positron!
It's about the processes and energy scales involved: Electrical resistance is scattering of the moving electrons with the lattice of atoms that makes up solid bodies. If the electron 'hits' an atomic core, it gives away some of its kinetic energy, which is transferred to the atom. Atoms of the lattice moving is called a 'phonon', and that is the microscopic description of 'heat'.
If you go to higher energy scales, it's different: In an X-ray tube, fast electrons hit the atoms of a metal target and are stopped abruptly. Their very high energy in the 10s of keV range is then converted to X-rays.
No, it's physics. Classical electrodynamics, well-known for more than 100 years now. There are very good books about it.
Rundmaus
What is making up the current is different: In a normal conductor, it's electrons. They are scattered at the atomic lattice, losing energy, creating the macroscopic physical quantity 'resistance'.
Electrons are so-called 'fermions'. That is a kind of elementary particle for which the 'Pauli exclusion principle' holds: That means no two fermions are allowed to be the same in all of their properties (energy, speed, place, ...).
Now, in a superconductor at very low temperatures, two electrons can couple via the atomic lattice, they 'notice' the presence of the other electron due to its influence on the surrounding atoms. The two 'coupled' electrons behave like a new particle, and this time it's a 'boson'. That's a particle that does not care about Pauli, as many bosons as like are allowed in the same state.
What happens in a superconductor then is that all electron pairs go into the state of lowest energy available, because the Pauli principle does no longer forbid it. From a quantum mechanical point of view, all these electron pairs can now be described as one 'large' wavefunction extending over the whole solid body. This wavefunction no longer 'sees' the small atoms and can not scatter with them. So the electron pairs move freely through the solid, there is no longer an electric resistance.
Rundmaus
Supers have the ultimate skin effect. The conductivity being infinite, the flow is on the surface.
A super has a specification called Ic...critical current, in amperes per square mm, say 1000 amps per sq mm.
If you take this super, and it's big say 10mm diameter, and put 1000 amps into it, the current will "consume" 1mm of area, that being on the surface into the conductor. If you put in 2000 amps, it will consume 2 square mm of area, so the current will go deeper into the conductor.
At some current level, exactly when the amount of current equals the critical current times the area of the conductor, you will have filled up the super. Any current beyond that level will cause the conductor to revert from a superconductor to normal material. We call that a "quench".
If a quench occurs, the resistance of the conductor times the current squared (power dissipation) will be very very large. If the power supply is not quickly turned off, the conductor will rapidly climb in temperature to 1060 degrees C where the copper will melt. Then, fun things start to happen.
This occurred at the LHC 2 weeks after startup. The resulting plasma ball converted all the stored energy of the machine into heat, vaporizing about 2000 gallons of liquid helium instantly.
That expansion caused the magnets in the tunnel to play leapfrog. They are about 50 feet long with about 1 meter diameter of almost solid iron the entire length, weighing about 45 tons apiece if I remember correctly.
The energy released was about the same as a 747 travelling 450 knots.
jn
I've a better understanding from these posts, but one question I have... what is it that causes "the electron pairs move freely through the solid" in a controllable way? (How) does it differ from the electron + hole movement from Physics 101?
I've often found it less headache inducing if you think of it this way - resistance defined as the change in voltage per change in current: R = dV/dI (differential equation)
By definition, V=IR is only good for linear systems, I believe, like an ideal resistor. Real resistors behave linearly in certain regions of operation.
It's been a long time since I've done this, so please correct me if I'm wrong.
By definition, V=IR is only good for linear systems, I believe, like an ideal resistor. Real resistors behave linearly in certain regions of operation.
It's been a long time since I've done this, so please correct me if I'm wrong.
- Status
- Not open for further replies.