Whoa! I'll drink to that! 🍺 🍺 🍺
Showing 20 responses by geoffkait
Allow me to summarize. It doesn’t really matter what the velocity of electrons is since they are only the charge carriers. It doesn’t really matter what direction electrons are traveling since they’re only the charge carriers. And compared to the velocity of the EM - even if one considered electrons were moving at Fermi velocity - the relative velocity of electrons is negligible. Recall that the velocity of light (photons) is constant even if it’s measured from a rapidly moving rocket ship. 🚀 |
Geoffkait: "Therefore in this wire the electrons are flowing at the rate of 23 µm/s. At 60 Hz alternating current, this means that within half a cycle the electrons drift less than 0.2 μm. In other words, electrons flowing across the contact point in a switch will never actually leave the switch." to which kijanki replied, "You’re talking AGAIN about electrons. Electric current moves with the speed of electric charge (electric field) and not the speed of electrons or drift velocity. When you flip a switch electric charge moves thru conductor at the speed of light (remember stacked balls?) magnetic wave follows at the same speed. If electric current moves at the drift velocity then in very long cable electrons at the end would not even move since it would take hours or days for charge to get there." >>>>>I never said electric current moves with the velocity of electrons. I already said I think electrons are the charge carriers. You are confusing me with someone else perhaps. then kijanki wrote, "All electrons along the wire move together instantly like stacked balls. Electric and magnetic fields have to move with the same speed (electro-magnetic field) because one doesn’t exist without the other. Again, imagine pipe filed with ping-pong balls. When you push them at one side of the pipe they will start coming out at the other instantly. When there is no change (DC) electrons move at drift velocity. DC current is proportional to drift velocity while drift velocity is proportional to magnitude of electric field. Any sudden change at the one end of the wire will travel thru the wire at the speed of light and it will arrive almost instantly and not a few days later. It will travel as wave of electric charge inside of the wire (stacked balls) and wave of magnetic field outside of the wire at the same light speed (or close to it)." >>>>>EM waves travel at light speed but magnetic fields are stationary. Magnetic fields are induced by the current traveling through the wire. It’s the right hand rule. I never said electrons carry the current. And I’ve always said the EM waves are comprised of photons. All EM waves are comprised of photons. That’s why they travel at lightspeed. |
No one has answered my question, why is there a "net velocity" for electrons? Assuming electrons move back and forth with alternating current, which I’m actually not convinced they do. Also, the Fermi velocity is the *directionally random* quantum mechanical velocity of electrons when no current is present. To refer to a Fermi velocity when current is present makes no sense since electrons then travel axially, I.e., not randomly. |
Exhibit A from the wiki page on Drift Velocity: Therefore in this wire the electrons are flowing at the rate of 23 µm/s. At 60 Hz alternating current, this means that within half a cycle the electrons drift less than 0.2 μm. In other words, electrons flowing across the contact point in a switch will never actually leave the switch. By comparison, the Fermi flow velocity of these electrons (which, at room temperature, can be thought of as their approximate velocity in the absence of electric current) is around 1570 km/s.[2] |
Kijanki wrote, Drift velocity is average electron velocity since it is "net" axial velocity in one direction while electrons move in different directions. https://en.wikipedia.org/wiki/Drift_velocity Fermi velocity (random) applies only to materials when no current is applied. As I stated previously the very low Drift Velocity indicates that electrons do not (rpt not) travel rapidly at any time in the conductor. If they did the net velocity or average velocity whatever would be much higher than the centimeter per hour velocity observed. Pop quiz, if electrons are changing direction with alternating current, why is there a net velocity in one direction along the axis? Shouldn’t there be zero net velocity? And why is the net electron velocity in one direction, not the other direction? Why do electrons favor one direction over the other, assuming vector of Drift Velocity is always in the same direction? |
almarg wrote, "now regarding, Geoffkait 9-2-2017 One thing I will sign up to is that if anything is traveling down the conductor it’s photons, not electrons. Free free to concur with comment, concur without comment or non concur. As I’ve stated on previous occasions, I agree fully that the energy of an electrical signal (or power) being conducted via wires is conducted at near light speed in the form of an electromagnetic wave that is comprised of photons. We’ll have to agree to disagree, however, as to whether those photons propagate within or outside of the conductor, aside from the very small fraction of the photons corresponding to the very small amount of energy that is absorbed by the resistance of the conductor and converted to heat. >>>>Uh, I’ve already stated that it’s a tie. As indicated by the mathematical paper from the Journal of Physics on the dodgy subject of whether the energy of the signal is located outside or inside the conductor the energy is actually partly outside and partly inside. And the mathematics for that conclusion is provided in the first couple of paragraphs. Don’t tell me you didn’t read it. GASP |
Al, sorry, but I prefer to not (rpt not) sign up to your explanation, either. For the same reason, actually, that I gave for not (rpt) agreeing with the drift velocity being defined as the average velocity. I.e., it doesn’t make sense. Please don’t put words in my mouth. If you guys want to agree to that explanation feel free to knock yourselves out. One thing I will sign up to is that if anything is traveling down the conductor it's photons, not electrons. Free free to concur with comment, concur without comment or non concur. |
How could Drift Velocity be the average electron velocity? That would mean some electrons travel *even slower* than one cm per hour. That’s not a typo. One cm per hour. And it would also mean that no (rpt no) electrons travel very fast. Otherwise, the average velocity would be much higher. If it doesn’t make sense it’s not true. In fact, electrons don't have to move at all for the whole thing to work. |
kijanki wrote, "Back to our analogy with balls stacked in the tube - last ball will start moving the same moment as first ball (they push each other). That’s electric charge moving (electric current)." No, actually that analogy intimates that current travels instantaneously, which cannot (rpt cannot) be true. I mean unless you’re invoking action at a distance. Current moves at *near lightspeed* which means current must be photons, no? The electrons are only charge carriers, they're not (rpt not) the charge per se. |
The "electron drift" IS the electron velocity. Drift velocity is on the order of cm per hour. In other words they, the electrons, are virtually stationary. The "drift velocity" is not (rpt not) the net velocity due to back and forth motion of the electrons. Whatever moves at lightspeed or near lightspeed are photons. You know, the only particles that can - and must - travel at lightspeed or near lightspeed. If you want to say current is an EM wave and therefore comprises photons I have no problem with that. Thus electrons are charge carriers, they are not the charge per se. |
One last thing. Over, I think it is on the Directionality of wire thread, someone posted a link to a largely mathematical article from, I believe it was the Journal of Physics, that described how energy travels down a conductor. The article was used by the posted to support the popular idea that energy travels completely OUTSIDE the wire, not inside the wire. Yet, that very article - in the first couple of paragraphs - states very clearly that energy is traveling both inside the wire AND outside the wire. The mathematics for both energies are subsequently described. I already acknowledged that (some energy travels outside the conductor) might be true a couple of weeks ago. Furthermore, based on that evidence, the mathematical evidence, I hereby declare this current argument a tie. The peer review tribunal can take a break. |
Typical velocity factors, numbers on left are percentages of velocity of light in a vacuum. Transmission line 95–99 Open-wire "Ladder" Line 83 RG-6 Belden 1189A coaxial cable 82 RG-8X Belden 9258 coaxial cable (foamed polyethylene dielectric) 80 Belden 9085 twin-lead 66 Belden 8723 twin shielded twisted pair stranded (polypropylene insulator)[10] 66 RG-213 CXP213 coaxial cable (solid polyethylene dielectric) |
As far as the directionality thread is concerned Al and Atmasphere have definitely not proved their points. Furthermore, it should be pointed out much of Al’s argument (as is often the case) is an Appeal to Authority, citing experts to support his argument. Even citing his own expertise, not to mention Atmasphere’s. That’s an appeal to authority. You know, a logical fallacy. Geez, all you would have to do to win any (rpt any) technical argument is say well, I found this guy so and so and he says such and such so I must be right. Cheers |
Let’s try a different approach. Teflon is obviously a very good dielectric material, right? It has a dielectric constant of approximately 1.0 if I’m not mistaken. Which means that electomagnetic waves will not (rpt not) be slowed significantly through Teflon. On the other hand, we know that the audio signal - which (I think there is agreement on this) is an electromagnetic wave - is found to travel only around 70-85% of the velocity of light in a vacuum. I believe this means that the electromagnetic wave must be traveling through the copper, not the dielectric. His else could you explain the discrepancy? |
If the audio signal travels through the *dielectric* and not (rpt not) through the metal conductor I suppose we can throw out the whole skin effect idea, which says most audio frequencies travel *inside* the metal conductor at some depth, with only very high frequencies, perhaps above "audio frequencies," traveling near the surface, I.e., skin. How can audio frequencies travel inside the conductor when the audio signal - the electromagnetic wave - travels outside the conductor? |