Electricity and electron spin

Post #42,889 by admin 6/19/02 11:35:37 AM Reply	Electricity and electron spin What do the two have to do with the other? Having a discussion with a self-proclaimed metallurgy expert who is claiming that electrons in electricity don't move at all, they just transfer "charge" and "spin". My understanding is that the electrons hop from atom to atom, utilizing the free energy states. Metals make good conductors because they have a lot of free states, and the electrons are free to move easily. That doesn't mean an electron starts in the generator plant and moves all the way to my house, but there is a hopping from atom to atom going on. Regards, -scott anderson "Welcome to Rivendell, Mr. Anderson..."
Post #42,892 by SpiceWare 6/19/02 12:28:45 PM Reply	Wouldn't expect it to with AC generation That doesn't mean an electron starts in the generator plant and moves all the way to my house With AC the electronics just oscillate back and forth in the wire. (Though I suspect it is possible for a specific electronic to only move "back" while another specific electronic is only moving "forth"). I believe the oscillating is what makes AC so much more effecient than DC for long-distance power distribution. Darrell Spice, Jr. [link\|http://home.houston.rr.com/spiceware/\|SpiceWare] - We don't do Windows, it's too much of a chore
Post #42,973 by ben_tilly 6/20/02 12:27:33 AM Reply	Why AC is more efficient You can transmit power more efficiently at higher voltages. Unfortunately high voltages are dangerous in end-user applications. With AC there is a neat device called a transformer which can turn a high-voltage, low-current current into a low-voltage, high-current one instead. Allowing you to transmit at an efficient voltage, and then deliver to houses at a safe one. DC doesn't have an equivalent, so safe voltages don't travel long distances. Cheers, Ben "... I couldn't see how anyone could be educated by this self-propagating system in which people pass exams, teach others to pass exams, but nobody knows anything." --Richard Feynman
Post #42,898 by Another Scott 6/19/02 2:14:29 PM Reply	He's mixing things up. Hi, Having a discussion with a self-proclaimed metallurgy expert who is claiming that electrons in electricity don't move at all, they just transfer "charge" and "spin". Electrons have properties like mass, charge and spin. They're moving all the time (as they're in orbits around host atoms). Current is due to the non-random motion of electrons. That is, an Ampere of current is defined as the net motion of 1 Coulomb of charge per second across some boundary. It's about 6.24e18 electrons/s. (See [link\|http://scienceworld.wolfram.com/physics/Current.html\|this page] at Wolfram for the definition of current and links to other terms.) Spin is important in other aspects of solid-state physics, but not in electrical current. My understanding is that the electrons hop from atom to atom, utilizing the free energy states. Yes. Electrons can only be in allowed energy states. One of the rules of quantum mechanics. Metals make good conductors because they have a lot of free states, and the electrons are free to move easily. Yes, but more precisely: Metals are good conductors of electricity because there are lots of available energy states, AND because the energy states are in a range that room-temerature electrons can easily reach. This differs from semiconductors like silicon in that there are a lot of available energy states in silicon, but there's an "energy gap" that prevents most of the electrons in the silicon crystal from being able to be in those energy states - the electron's don't have enough energy to be there. In silicon the energy gap is about 1.1 eV, while in metals the energy gap is very small or zero. It's this energy gap that makes it possible to control the conductivity of semiconductors (by "doping") and is what makes things like p-n junction diodes, npn transistors, etc., possible. That doesn't mean an electron starts in the generator plant and moves all the way to my house, but there is a hopping from atom to atom going on. Yup. HTH. Cheers, Scott.
Post #42,902 by admin 6/19/02 3:37:05 PM Reply	Well, spin does have a related effect... Magnetic moment... and electricity can be generated by moving magnetic fields. But that has nothing to do with standard AC. :-) Regards, -scott anderson "Welcome to Rivendell, Mr. Anderson..."
Post #42,904 by admin 6/19/02 4:23:56 PM Reply	Re: Electricity and electron spin Well, here's the support he gave: [link\|http://www.slb.com/seed/en/ask/q_and_a/resist.htm\|here] Which basically says that electrons exist as a pack of waves, interacting with the metal lattice. However, it doesn't say anything about transferring energy via spin. Regards, -scott anderson "Welcome to Rivendell, Mr. Anderson..."
Post #42,975 by ben_tilly 6/20/02 12:32:32 AM Reply	Your self-proclaimed "expert" is a jackass Current by definition is the movement of charge. Charge moves because charged particles (mainly electrons) have net motion. The actual velocity of the electrons is miniscule, but still... Cheers, Ben "... I couldn't see how anyone could be educated by this self-propagating system in which people pass exams, teach others to pass exams, but nobody knows anything." --Richard Feynman
Post #46,257 by tablizer 7/20/02 11:51:29 PM Reply	Is it all relative? Perhaps there is no way to tell the difference between a particle changing position and a particle "giving" its attributes to another similar particle. We don't know whether the memory address (or record ID) is the same, we can only see the attributes of the things. Thus, whether it is a movement or an attribute transer, it looks the same to the observer? ________________ oop.ismad.com
Post #46,260 by ben_tilly 7/21/02 12:10:49 AM Reply	Sorry. We can tell Hypothetical science questions have a nasty habit of having answers. If the particle changes position, its charge moves and the movement of charge has visible effects (eg magnetism). By contrast the ripple of communications from one charge bumping the next bumping the one after and so on can be measured moving from point A to point B. The former goes at walking speed, the latter at near the speed of light. So both happen, and we can tell the difference. Cheers, Ben "... I couldn't see how anyone could be educated by this self-propagating system in which people pass exams, teach others to pass exams, but nobody knows anything." --Richard Feynman
Post #46,816 by deSitter 7/25/02 10:30:16 AM Reply	Identical Particles A metal is a collective thing. You can't really talk about individual electrons. Instead, the metal is a sort of lattice surrounded by strange "gas" of electrons. Inside the metal the charge is on the average zero - all the free charge moves to the surface almost instantly (this is why you are safe inside a car or a Saturn V that gets hit by lightning) and can be siphoned off to ground without changing anything inside. But the lattice centers of a pure elemental metal are positively charged - the nuclei - and the equal and opposite charge of electrons adopts a mass collective behavior and interaction with this lattice that is completely unclassical because you can't describe it as an ensemble of simply countable things (Maxwell-Boltzman statistics). Instead they obey a weird antisymmetry under interchange (Fermi-Diracs statistics). The statistical behavior of large numbers of Fermions simply cannot be understood by any classical analogy. Charge and spin are, in four dimensions, independent ideas. Spin (angular momentum in general) is a more fundamental idea, like mass, that has to do with the invariance ideas that give order to spacetime. You can say, spin is kinematical (connected with spacetime invariance), while charge is dynamical (connected with invariance of electromagnetism under a class of "gauge transformations"). Interestingly, you can extend the world from 3+1 dimensions to 3+3 and suddenly charge is an aspect of angular momentum in the bigger space. A unification like this is called a "decontraction" and resembles the unfication of electricity and magnetism on "decontracting" space and time.
Post #46,823 by imric 7/25/02 11:10:56 AM Reply	smile Good to see you posting again... Imric's Tips for Living Paranoia Is a Survival Trait Pessimists are never disappointed - but sometimes, if they are very lucky, they can be pleasantly surprised... Even though everyone is out to get you, it doesn't matter unless you let them win.
Post #47,000 by static 7/26/02 8:20:55 AM Reply	If you ever do a Hawking and publish a readable book.. ... do us a favour and let us know, huh? :-) Wade. "Ah. One of the difficult questions."

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