How fast does an electon move? - Page 1
Forum section: electronics / projects

author: John Heath
author_rank: Frequent Contributor
timestamp: December 03, 2016, 03:13:04 am
content: One ampere is approximately equivalent to 6.2415093×10^18 elementary charges moving past a boundary in one second according to Wikipedia.I have a current meter that will measure the strength of a magnetic field only and from that information can predict current in amps as magnetic field equals current of electrons moving past a boundary as stated in wiki quote. I will put 1 m amp , 6.2415 x 10^15 electrons , through a copper wire . Electrons are moving on average 1 inch per second , ball park number. The magnetic field is X therefore current must be 1 m amp. I will now adjust the CRT current of a small black and white TV to 1 m amp , 6.2415 x 10^15 electrons. I will place the same current meter around the CRT neck and it will measure the magnetic field as X therefore the current is 1 m amp. The velocity of the CRT electrons at the neck is 10 to 20 percent c not 1 inch per second. You see the problem. The magnetic field is independent of the electron velocity for the same number of electrons 6.2415 x 10^15. However if the electrons always move at c in either random direction or somewhat averaged in one direction then the problem goes away. Does this mean that the electron is always moving at c regardless. If there something wrong with the logic I am using. I would like to know what others think. How fast does an electron move?

author: Nerull
author_rank: Frequent Contributor
timestamp: December 03, 2016, 04:22:42 am
content: As a particle with mass, it is not possible for an electron to move at c.

author: David Hess
author_rank: Super Contributor
timestamp: December 03, 2016, 05:45:04 am
content: You are looking fordrift velocity. In common situations with copper wire it is incredibly slow.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 03, 2016, 06:26:08 am
content: Thank you for taking the time for a long answer evb149 and Nerull I hear you , can not go c if you have mass.I am going to have some more fun with this. I am now in space with 2 magnetic probes and 1 electron. The electron wizes past the first magnetic probe and measures a magnetic field around the electron. The second magnetic probe is moving with the electron and measures no magnetic field around the electron. Two identical magnetic probes yet one says magnetic field around the electron and the other says no magnetic field around the same electron. The only difference between the probes is one is moving with the electron and the other not. How can magnetism be real if the magnetic field magically disappears when you catch up to the electron ? The electric negative field , Coulomb force , of the electron is real as my movement relative to that field can not make it disappear. This is not true of a magnetic field as I can make it disappear by catching up the the electron. A magnetic or electric field in a vacuum is either real or not real in that vacuum. . In the case of a magnetic field does not seem to be real if it is only there when I move relative to a charge. I am open to counter arguments on this as I am not entirely sure I have it right.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: December 03, 2016, 06:36:13 am
content: Analogy: I'm holding a flaming torch, therefore I'm warm. I walk past someone stationary, who warms up from the torch then cools off as I leave. Yet I'm warm all the time. Is heat real? For whom is work being done?Put it another way; when I went and picked up the flaming torch, I warmed up. Eventually when I set it down, I'll cool off.

author: David Hess
author_rank: Super Contributor
timestamp: December 03, 2016, 07:54:00 am
content: I like this analogy: if I have a tube full of marbles and I add a marble to one end forcing another marble out the other end, how fast are the marbles moving?The most sensitive circuits I have regularly worked with had a bias current of 2 femptoamps which is about 6000 electrons per second.

author: Marco
author_rank: Super Contributor
timestamp: December 03, 2016, 09:23:42 am
content: I'm curious, how fast does an electron move in ye average through air static spark?

author: DTJ
author_rank: Super Contributor
timestamp: December 03, 2016, 09:29:05 am
content: Quote from: Marco on December 03, 2016, 09:23:42 am...and how far?

author: IanB
author_rank: Super Contributor
timestamp: December 03, 2016, 09:44:23 am
content: Quote from: John Heath on December 03, 2016, 03:13:04 amSo far, I don't see a problem. What problem do you see?Try a simple thought experiment.Let's measure the rate of traffic flow on a road by counting the number of cars that pass a boundary every second. Let's call this the traffic current.Road A is a suburban road, and on this road we count one car per second passing the boundary. So the traffic current is one car per second, or 60 cars per minute. On this road the cars are moving at an average speed of 20 mph.Road B is a major highway, and on this road we also count one car second passing the boundary. So the the traffic current here is also 60 cars per minute. However, on this road the cars are moving at an average speed of 70 mph.Does our intuition here also have a problem? I suggest not. We are very familiar with roads, and therefore everything seems fine.The explanation, if we look for it, is that on road A the individual cars are bunched up close together with small gaps between them. We could say the traffic density is higher. Whereas on road B the cars are much more spaced out with larger gaps between them. Here the traffic density is lower.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 03, 2016, 09:58:59 am
content: My recollection is that a human can outrun the drift velocity of electrons in copper even at current densities sufficient to melt the wire.The other puzzle is interesting, it might be tied into the "Faraday Paradox" , the fault with this paradox relies on the way humans draw a magnetic field on paper with lines, and then infer that moving these flux lines will push on a wire. In actual fact a magnetic field can't move, its like gravity, the gravity field doesn't rotate with the Earth. You can make all sorts of homopolar motors that display the paradox, they are great for confounding high school physics teachers.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 03, 2016, 02:11:12 pm
content: Quote from: Paul Moir on December 03, 2016, 06:36:13 amYes but in the case of the magnetic field , heat , the flaming torch , electron , is cold when I try to warm my hands. Only when I run past the torch can I feel the heat. Or I can stand still and have the torch move this way or that to feel the heat. It is as if movement relative to the torch causes heat not the torch itself. An electron can be right next to a strong magnet and not be effected. If it move it will but not if it stands still. However the charge of the electron is always there moving or not. My 2 cents this means the charge , Coulomb force , is real but magnetic field is not real in the sense that you can not feel the heat of the flame if not moving.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 03, 2016, 02:27:06 pm
content: Quote from: David Hess on December 03, 2016, 07:54:00 amIf your circuit at 2 f amps per second was sensitive to .002 f amps then 6000 electrons would be 6 electrons per second. Would you start to hear a ticking sound of individual electrons at 6 per second. If so then your 2 f amp circuit should be make noise in the 6 KHz audio range as electrons pass by. It would be interesting to see if this is true.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 03, 2016, 02:39:36 pm
content: Quote from: DTJ on December 03, 2016, 09:29:05 amThis is a great question. Electrons thrown off by the sun can take days to arrive at earth. However this is not a static spar. More like throwing as base ball. How fast are electrons moving in a lightning strike? I can say the the impedance to the electron in a static spark is low. I connected a neon bulb to a 5 amp fuse then plugged it into a wall socket. The 5 amp fuse blew so fast that it was black on the inside of the glass. This would mean that a lightning strike sees the air as a short circuit when in the heated plasma tube of the lightning strike.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 03, 2016, 03:00:41 pm
content: Quote from: IanB on December 03, 2016, 09:44:23 amCars moving at 20 MPH generate a puff of wind when passing by. Cars at 100 MPH generate a greater puff of wind when passing by. I will call this puff of wind the magnetic field generated by an electron passing by. My magnetic clamp probe can only measure the puff of wind , magnetic field. 100 electrons moving at 20 MPH or 100 MPH are generating the same puffs of wind regardless of their speed and therein is the problem from my shoes. I say this as my magnetic probe will always tell me what the current is regardless of electron velocity.

author: TimFox
author_rank: Super Contributor
timestamp: December 03, 2016, 03:20:30 pm
content: In solids, there is an important parameter "mobility" that applies to charge carriers.See:https://en.wikipedia.org/wiki/Electron_mobilityIn general, there is a different mobility for positive holes and negative electrons in the device. The drift velocity is proportional to the electric field, with the proportionality constant called the "mobility" for that carrier. Note that holes moving to the left and electrons moving to the right in response to a field pointing to the left both give a net current to the left. The drift velocity is limited by scattering off the atoms in the lattice. Otherwise, applying a field to a charge carrier gives a net acceleration, rather than a limited velocity.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 03, 2016, 04:00:38 pm
content: Quote from: evb149 on December 03, 2016, 02:56:36 pmThis brings to mind Mr Red LED. It is somewhat like a diode with a forward voltage drop of a little over a volt. If one electron jumps the voltage barrier of this LED the energy of this event would be the current in amps of 1 electron time the voltage drop of 1 volt. This energy is radiated away as a photon. This means the energy of that photon for this event of 1 electron hop is the energy of voltage 1 times current or 1 electron. I have that at 6.2415 x 10^-18 amps times 1 volt for an event energy of 6.2415 x 10^-18 Joules. Here is where it gets interesting. Mr Planck says if I divide that number by his constant h it will tell me the frequency of that photon for that amount of energy. E=fh so f=E/h therefore 6.24 x 10^-18 Joules divided by h 6.62 × 10-34 = 942 X 10^18 CPS .I think I forgot to carry the 2 somewhere ?? In any event if I did it properly the frequency in cycles per second would equal red light. How cool is that.

author: David Hess
author_rank: Super Contributor
timestamp: December 03, 2016, 05:27:19 pm
content: Quote from: John Heath on December 03, 2016, 02:27:06 pmIn most cases circuits like this rely on integration so all high frequency content is removed and current and voltage noise are not important except at very low frequencies. The current noise over a 1 Hz bandwidth was specified to be 1/10th of the input bias current so still 2 orders of magnitude too great to see 6 electrons per second anyway.Leakage is obviously an important consideration and if an air dielectric capacitor is used, cosmic ray impacts will affect the output because of its great capture volume so a Teflon dielectric capacitor is more suitable despite higher leakage.This is not exactly what I was doing butthis articlediscusses these issues.And that article points to anarticle from Keithleywhich shows how to get down to attoamps but again through integration at low frequencies.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 03, 2016, 05:57:30 pm
content: There's on the order of 10^24 cm^-3 electrons in a metal, and only (current) many in the vacuum. So those in the vacuum must be going faster -- indeed, that many times faster!In semiconductors, where the carrier density is smaller than a metal (on the order of 10^18 cm^-3), the velocity must be higher, and other effects are more prominent, like the Hall effect (magnetic field deflecting the path of current flow within a solid). (This is how integrated Hall effect sensors are so common today.)When the greater velocity (in a semiconductor) interacts with the material properties, interesting things happen, like impact ionization (the cause of avalanche breakdown in silicon), or saturation (the cause of negative resistance in bulk doped GaAs -- Gunn "diodes").Tim

author: John Heath
author_rank: Frequent Contributor
timestamp: December 03, 2016, 09:56:46 pm
content: Quote from: evb149 on December 03, 2016, 03:20:02 pmGreat links for the subject at hand. With so many roads to go down I feel liberated to pick one I like. "does-special-relativity-make-magnetic-fields-irrelevant". This one requires length contraction , a Minkcowski idea. A little history. Minkowski was Einstein's old math teacher that thought little Albert will never amount to anything with his odd ideas and drifting mind. Years later when a giant in physics , Planck , is taking an interest in little Albert Mr Minkowski comes out of the wood word as Einstein's best friend with a hand stretched to shake the hand of the great Dr Planck. Sound like a fair weather friend to me and lets face it Minkowski , a fine mind to give this balance , was not an Einstein. Unfortunately the length contraction Minkowski interpretation of special relativity had the star trek appeal of 4 dimensions and became the way it is taught in schools today. The original paper on the electrodynamics of moving bodies uses an increase in the Coulomb force at right angles only without the need of a fourth dimension. I will now get off my soap box. In either case the magnetic field can be written off as a Coulomb force only therefore a magnetic field is no longer a fundamental force in nature. Good reddens as it is one less to worry about.

author: orolo
author_rank: Frequent Contributor
timestamp: December 03, 2016, 10:07:42 pm
content: Quote from: John Heath on December 03, 2016, 06:26:08 amVery good point, I wondered at this when first studying relativity. My understanding is that looking at the moving electronsin a wiredoesn't tell the whole story. The charged ions in the metal also count. The wire is electrically neutral because there are two currents, one of electrons and one of holes, with opposite charges and opposite velocities. The total current in the wire is the sum of both currents: since the charges are opposite, and the velocities are opposite, both add constructively and give the total intensity on the wire.Mathematically, if N is the number of moving electrons, v their speed, and e the electron charge:I (electrons) = e · N · vI (holes) = -e · N · (-v) ) = I (electrons)So, I (total) = I (electrons) + I (holes) = 2 · e · N · vNow, if you are comoving with the electrons, they are at rest, but the holes move at twice the speed:I (total comoving) = I (electrons comoving) + I (holes comoving ) = e · N · 0 + (-e) · N · (-2v) = 2 · e · N · v = I (total at rest)That is, the current doesn't change. Maxwell's laws hold, after all.Of course, matters would be different if you followed a beam of free electrons. In that case, if you comoved with the beam, you would experience a pure coulomb field from the beam, but no magnetic field.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 03, 2016, 10:32:45 pm
content: There are no holes in a metallic conductor, and the fact that there are holes in some types of conductors doesn't change the fact that there is an overall current flow. Indeed, holes have opposite charge and direction, so they contribute identically to the same positive current.There is nothing violated about relativity, regardless: indeed, for the same reason that a transformer exists and that a motor is merely a rotating transformer, one must necessarily expect to measure different amounts of fields (E vs. M) when moving relative to a source!It was this insight, that E and M are interchangeable under relative motion, and that no motion can affect the observed speed of light, which led inexorably to the discovery of Relativity.Tim

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 03, 2016, 10:40:00 pm
content: And EVB149's wiki article links tohttps://en.wikipedia.org/wiki/Faraday_paradox.If you build the homopolar motor/generator in figure1 (easily done with a D-cell , disc magnet, drywall screw, and a piece of finely stranded wire ) you can test it yourself.That it worked at all was a paradox to Faraday.But the interesting thing is that the motor works the same whether the magnet is stationery(magnet stuck to battery) or if the magnet is rotating (magnet stuck to the drywall screw) , so what you do is show some smart-arse with a PhD the motor operating with the stationary magnet, and ask "how does this work" he will provide some condescending answer (that usually requires a stationery magnet) then you swap the magnet around and ask whether it will still work, then apply power and prove him wrong.The important takeaway is that a magnetic field does not move, you can change its amplitude and its direction and that's all. The profile of a magnetic field can move, but the field is stationery (technically the field is not an "it", so "it" can't have attributes of position or velocity), similar to the way a wave travels across water without carrying water with it.Also you don't need electrons for a magnetic field, a radiowave propagating through a vacuum generates a magnetic field (and an electric field) as it races past.* drywall = plasterboard= gyprock

author: orolo
author_rank: Frequent Contributor
timestamp: December 03, 2016, 11:27:42 pm
content: Quote from: T3sl4co1l on December 03, 2016, 10:32:45 pmI was not meaning 'holes' in the semiconductor sense, but referring to the charged atoms in the metal conductor. A conductor is formed by charged atoms and a gas of free electrons in the valence band. The whole is neutral.The paradox is: it's a fact that a flow of moving charges in a wire generates a magnetic field. But the electrons in a conductor move very slowly. So if I walk at the same speed than the electrons and parallel to the wire, the magnetic field should disappear. And that doesn't happen! Why? The answer is that, while the electrons are not moving relative to you, the charged atoms are (with opposite charge and velocity), so you still measure the same current, and experience the same magnetic field. But this magnetic field is now generated by positive charges moving in the opposite direction, and that was I was calling 'holes'. I was using the electron/hole language, typical for semiconductors, in this situation, with a slight change for the meaning for 'hole'.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 04, 2016, 12:14:02 am
content: Quote from: orolo on December 03, 2016, 10:07:42 pmI was going to jump in and say no no the hole will generate the opposite magnetic field. However after reading your words "charges are opposite, and the velocities are opposite" I see your point. It is a double opposite. The hole is positive , opposite , but the direction of movement is also opposite so it complements the negative electron movement to generate the same magnetic field. Well done. I am going to write that down to not forget. I am sensing a little mischief in your mathematics. If you think this is leading to some boring constructive criticism you are right and apologies in advance but I admire your thinking.A hole stated as a positive charge must be consistent in the math as a hole that has a positive charge. This being the case the copper wire is now made of protons + , holes + and electrons -. You see the problem? The wire now has a net positive charge and will generate a magnetic field if moved. Moving wires do not generate magnetic fields.There is a way around this if the hole is defined as a preferred Coulomb position where the electron , emitter , could be in the future , absorber. The cost of this compromise is every electron must be accompanied by a hole that represents its future. Can not have holes moving without the same number of electrons moving the opposite way. This way the copper wire has a charge of 0 so we are off the hook for copper wire net charge. When not sure it is always a good policy the leave the door open to place the finger of blame on someone else. I would like to say that this is a Feynman time symmetry idea not my thoughts. Unless it works in which case it was my idea , ha.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 04, 2016, 01:48:03 am
content: Quote from: salbayeng on December 03, 2016, 10:40:00 pmYour direction of relative motion is wrong.A magnet is rotationally symmetric on its axis: there is no change in flux when a uniformly magnetized piece of material is rotated parallel to its magnetization (and also has a shape that's symmetrical on the same axis, which is the case for the average cylindrical magnet).Consider an array of spinning tops: rotating the table they are spinning on, has no effect on the total angular momentum of the ensemble. Each top continues to spin as it will (until friction takes its toll, of course). You can change the arrangement of tops, but if the arrangement itself is circularly symmetric (hence the requirement for a round, axially magnetized part), there isn't even a change in the distribution of angular momentum that's sitting on the table!Of course, magnets don't "spin", but the quantum phenomenon that they exhibit is similar enough that it was given the same word!If you imagine a magnet as always spinning, then the riddle of the homopolar generator becomes laughably trivial -- of course it doesn't matter whether the magnet spins, it's always spinning!The rotation of the disc, itself, is a fine example of relative motion. Note that rotating motion is accelerating motion, so it doesn't have the properties of relativistic inertial frames, it's more complicated -- but the point is it experiences a radial electric field, which isn't present in the (unaccelerated) reference frame.There's nothing wrong with this difference -- indeed again, it's necessary; energy can be drawn from that electric field, which induces a force on the rotor, and thus there is a conversion between mechanical and electrical energy.Tim

author: John Heath
author_rank: Frequent Contributor
timestamp: December 04, 2016, 03:04:48 am
content: If I hold the magnet and copper disk still and just rotate the contacts to the copper disk it will generate a voltage . I saw it in a yahoo video.A question. If I glue the meter to the copper disk and solder the leads to the outside and center of the copper disk will it generate a voltage on the meter that is rotating with the disk?

author: IanB
author_rank: Super Contributor
timestamp: December 04, 2016, 03:41:49 am
content: Quote from: John Heath on December 04, 2016, 03:04:48 amThis is because the wires leading to the contacts are moving through the magnetic field.

author: IanB
author_rank: Super Contributor
timestamp: December 04, 2016, 03:46:48 am
content: Quote from: T3sl4co1l on December 04, 2016, 01:48:03 amThis analogy is not quite perfect.If I place an array of spinning tops around the edge of a stationary circular table, each top spinning at 300 rpm, say, and then subsequently I start rotating the table at 10 rpm, then in fact each of the tops is now spinning at 310 rpm relative to a stationary observer outside the table. This means the tops do have an increased angular momentum as measured by that observer.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 04, 2016, 03:50:21 am
content: John,It has to slide to get any EMF, so soldering to 2 points won't work (unless the solder is molten!)you need to have relative motion to work.(I'm talking about motor action below as its easier to explain, but generator action is just the same)The critical feature of the setup is you must have one stationary arm (the return leg of the circuit through the meter) and one moving arm . If both arms are stationery you generate a torque on the lower leg, exactly balanced by a torque on the return leg (These torques generate a couple but the rotation axis of the couple is horizontal, so no net motion about a vertical axis.)You can spin the magnet about the vertical axis and nothing changes. Also there is no reaction torque experienced by the magnet (the return wire experiences the reaction torque.As a generator: if you have the forward leg rotating, and the return leg also rotating, basically the integral of induced voltage around the loop sums to zero.Faraday's original set up had a puddle of mercury with a wire arranged so it could circulate near the periphery of the puddle. A geometry very similar to the YouTube arrangement.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 04, 2016, 03:56:39 am
content: Quote from: IanB on December 04, 2016, 03:41:49 amExactly right ,It's a complete electric circuit.You can move either the disk ,( the lower half of the electrical circuit).Or move the "wires leading to the contacts" ( upper half of the circuit).Both results will be identical.(edit) and about 1/3 down herehttps://en.wikipedia.org/wiki/Faraday_paradox, the section onmodern explanationstalks about this.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 04, 2016, 04:37:56 am
content: Getting back to the moving electrons with an apparent magnetic field.Lets take two parrallel streams of electrons, zooming down a vacuum tube, horizontally either side of the centreline.If both move the same direction (e.g. as pairs) they will diverge due to coulomb repulsion,An observer moving with them will see no magnetic effect.A stationery observer will see two magnets aligned parrallel to each other and they will be repelled by both magnetic and coulomb repulsion.So beam divergence depends on the relative motion of the observer? doesn't sound right to me, but anyway, continuing on...If moving in opposite directions each electron will appear as a tiny magnet from the other's perspective (with north at the front and south at the rear??) . So assuming you are an observer on one electron, your won't see yourself as a magnet, and (assuming the other is approaching on your left),as youapproachyou will slow down (coulomb repulsion) and then passing through the front of the others magnetic field you get deflected up.As yougo abeamyou get deflected right due coulomb,andbehindthe other electron you get accelerated (coulomb) and deflected down (Lorentz). So as you pass a stream of electrons you will be wiggled up and down, and continually deflected right.From your perspective (and momentum conservation) the other electron must also wiggle as it is a magnet experiencing a Lorentz force due to a moving charge (i.e. your electron) .Of course the other guy sees you as a magnetic field, and himself as a charged particle.(Edit) If the electrons are wiggling up and down they should be radiating synchrotron radiation ? That should be observable?https://en.wikipedia.org/wiki/Synchrotron_radiation

author: John Heath
author_rank: Frequent Contributor
timestamp: December 04, 2016, 04:57:13 am
content: That is interesting. This would mean a meter on the table with sliding contacts will measure volt but the meter glued to the disk with leads soldered to the copper disk will not. What happens when both the stationary meter with sliding lead and the rotating meter lead soldered are both at 12 o'clock? The stationary meter would measure a voltage but the rotating meter would measure 0 volts . That would make for a cool picture to see one meter say .1 volt and the other rotating meter say 0 volts while measuring the same points on the disk at the same time at 12 o'clock on the rotating copper disk.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 04, 2016, 07:44:28 am
content: John,If I take some figure 8 cable, connect to a DMM, then short the other end of the cable, it will always read zero no matter how you wave the cable around in a magnetic field, that should be obvious .You could glue that cable and meter to any motor shaft and it still reads zero.You could solder the end of that cable somewhere on the rim of your homopolar motor, and it still reads zero.You could solder some other part of of the cable to some other place on the homopolar disk, and it still reads zero.You could cut the piece of wire that bridges two points soldered above, still reads zero, and this is exactly the meter glue to homopolar motor arrangement.andIf I take some figure 8 cable, connect to a DMM, then short the other end of the cable, it will read zero.if I place this cable into a strong magnetic field, then split the cable with a knife, and slowly pull the red wire apart at constant velocity, while keeping the black stationary, then I will read a fixed voltage on the DMM, lets say after I have spread the wire out to a foot or so, I rapidly solder a new red wire in adjacent to the black wire, and cut the original red wire, I now move the new red wire away from the black and read a constant voltage, so if you do this repeatedly (and do the wire changeover sufficiently fast,) you will read a constant DC output.A different variation would be to have an axle with say ten rigid wires arranged as spokes, the DMM negative lead connect to the axle, The positive lead has two jumper climps. So as the spokes revolve in a magnetic field you attach one crocodile clip to the nearest spoke, and as another spoke approaches you attach the other croc clip to this, then remove the first croc clip, and transfer this to the third spoke when it approaches, this way you have at least one lead attached to a moving spoke at all times and you will get a constant DC output.Let's repeat with a 100 spoked wheel, and use wire brushes to pick up the nearest spoke, again you will get a constant DC output.You could extend this to a thousand spoked wheel, which is essentially a solid disk.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 04, 2016, 05:28:59 pm
content: Let's repeat with a 100 spoked wheel, and use wire brushes to pick up the nearest spoke, again you will get a constant DC output. You could extend this to a thousand spoked wheel, which is essentially a solid disk.I see a fly in the soup here. Instead of moving the clip from spoke to spoke I will use a FET analog switch to move from spoke to spoke. As a analog FET switch requires zip in the way of energy to switch from spoke to spoke a voltage resulting from this would be free energy assuming the copper disk is not rotating . Check mate. As there is no free lunch . free energy , in physics there should not be a voltage. I will be clearer in details to make sure we are one the same page.The magnet is not rotating. The copper disk in not rotating. The 100 spokes soldered to the outside of the disk are not rotating.The only thing that is rotating , effectively , is the 100 analog switches selecting one spoke at a time in a clockwise direction.You are saying this will produce a voltage?

author: IanB
author_rank: Super Contributor
timestamp: December 04, 2016, 05:54:57 pm
content: A voltage is not energy (i.e. power output). Also a switch does require energy to change state, whether an FET switch, or even a diode.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 04, 2016, 07:50:06 pm
content: Spokes will not generate a voltage no matter how many of them you select from. Relative motion is required.Otherwise, there would be static voltage on the spokes, and switching them in with transistors would work. Indeed, switching them wouldn't even be necessary, you could just sit there and soak.Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 04, 2016, 08:05:46 pm
content: A perhaps related paradox is adiabatic expansion/compression:Intuitively speaking, compression/expansion of a gas feels natural, when you have many particles (a gas) in a box. The gas presses on the walls at all times, and no matter how fast the walls move, they are exposed to a quasi-continuous force.But it seems to intuitively fail for a single particle. Suppose you move the piston at such a speed, so that the lone gas particle does not interact with it during the move. In one moment, the gas particle bounces off the piston in one position, and in the second moment (after the move), it bounces off at a different position. Yet it's still going the same velocity, and therefore is at the same temperature, so hasn't been adiabatically expanded or compressed.Have you just violated adiabatic conditions, then?Assume the chamber walls do not exchange heat energy with the gas, i.e., it's a closed system with insulating walls.The resolution is thus:Thermodynamics is only concerned with the eventual result of change. "Eventual" as in, infinite time. But implicit in this assumption is that, any possible change can only happen continually. And it is the sum of those derivatives that matters. Thermodynamics is about integrals of a system over all time.Moving the wall "instantaneously" (as far as the gas is concerned -- it doesn't need to be a contrived instantaneous event, it can be a real continuous physical movement as long as the gas bounce period is known) violates this condition, because the system is now discontinuous. So it violates the assumptions, not the conclusions!In E&M, when Faraday's law tells you that the voltage is the derivative of flux, it's not something that can be constructed in piecewise manner -- it's a true, physical derivative. You can't have voltage without relative motion, whether it's change of the field (as in a transformer) or geometry (as in a motor).Tim

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 04, 2016, 11:23:05 pm
content: TimI think you skipped this bit "So as the spokes revolve in a magnetic field ",The reason you need the croc clips is because the spoke moves too far away to reach anymore, and you need to clip onto the next spoke as it comes past.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 04, 2016, 11:38:23 pm
content: it's not something that can be constructed in piecewise mannerI hear you and agree. FET switches are rotating in a piece-wise manner not real rotation so it is not the same.I am going to make a bazaar statement then do my best to dig a way out of that hole.The bazaar statement.The true volt drop from the middle to the outside of the copper disk in a magnet field is millions of volts without the need to rotate.Onward with shovel in hand. I will charge an air plate condenser to 100 volts. I can measure the voltage from plate to plate as 100 volts. However if I move inside the condenser between the plates I can no longer make this measurement as I and my meter are inside the voltage gradient of the condenser. I will always measure 0 volts between the condenser plates from the inside the condenser between the plates. There is an example of this in sky charge. Our sky charge is around 100 volts per meter. That is 200 volts from head to toe. If you measure from head to toe the reading is 0 volts. It is 0 volts as we are in the voltage gradient of our sky therefore it is a measurement that can not be made.The magnetic field creates a voltage gradient around the copper disk of high voltage but this voltage can not be measured as you have to enter the same voltage gradient to make the measurement. However a small amount of movement takes us slightly out of this voltage frame of reference allowing us to measure a tiny amount of this 1 M volts gradient from the center to the outside of the copper disk.This requires a blind belief that special relativity has is right that a magnetic field is just a Coulomb force caused by relative movement.

author: nuno
author_rank: Frequent Contributor
timestamp: December 05, 2016, 12:40:41 am
content: To the OP:http://www.physlink.com/education/askexperts/ae69.cfmhttp://amasci.com/miscon/speed.html

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 05, 2016, 12:42:14 am
content: Hi John, it is customary to use an emoticon when having a leg pull.else people might think you are serious.Quote from: John Heath on December 04, 2016, 11:38:23 pmActually not true , you can measure the voltage of a capacitor while inside the electric field of said capacitor.You can also measure the voltage induced in a coil rotating withaxis perpendicular to a magnetic fieldwhile sitting in that coil.You can measure the strength of "gravity" while sitting in a gravitational field.These issues are all basically "geometry" issues , in order to assign a number to a measurand, you may need to perform some kind of integral over a path. Take a simple example, with say constant current flowing down a resistive wire, the path integral is simply the distance along the wire between the meter probes.The homopolar motor has a really odd geometry (the "physical" area is constant, but the "electrical" area always increases, think of a hamster wheel, if the wheel is 100mm diameter and 50mm wide, the physical area available is 1670sqmm., but if the hamster does one revolution per second, the area he sees increases by 1670sqmm every second) . If you can get your head around how a hamster can be simultaneously running at 570m/hr and be stationary then you are halfway to understanding a homopolar motor.Have you ever wondered why it is that you can't hear yourself in the earpiece of a telephone? It is because there is a coupling transformer, the wire with the microphone signal goes into transformer, round and round the core several times then gets sent out on the pair of wires connecting your phone to the other guy. The incoming signal to your phone goes round and round through the same transformer before getting to the earpiece, effectively cancelling out your own voice. Basically the path integral from the microphone to the earpiece is zero, inspite of the large fluctuations in the magnetic flux of the transformer. Because the microphone wire and earpiece wire travel the same path there is no net signal.It analogous (but not equivalent) to not measuring a voltage while sitting on a homopolar rotor, while "the other guy" can measure a voltage.(note to E.E.'s reading this, I'm aware how sidetone cancellation actually works).

author: John Heath
author_rank: Frequent Contributor
timestamp: December 05, 2016, 12:45:45 am
content: My use of a condenser was not the best example for this case. A sphere 1 meter in diameter. Another sphere 2 meters in diameter. The two spheres are 1 meter apart. It will be around 10 p farad between the spheres. Charge the two sphere to 1 million volts. At 10 p farad we can keep track of how much energy was put into the spheres. Now place the 1 meter sphere inside the 2 meter sphere without shorting them out. Once the little sphere is inside the big sphere it can not be shorted out even if the little sphere touches the inside of the big sphere. I repeat for clarity. The little sphere inside the big sphere can not be discharged even if it touches the big sphere. Now take the little sphere out of the big sphere and place them back the way they were 1 meter apart. A measurement will show the the energy 1 M volt at 10 p farad is still there and can be discharge. This one you can take to the bank as I have a video of it. I will dig it up so you can have a gander.Found it

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 05, 2016, 01:02:35 am
content: Tim, re "adiabatic" ,There are other areas of physical science where "adiabatic" can be invoked to explain a lossless transformation.An example inspired by a recent post, and a good way to trap unwary physics students.First pose a problem: A parallel plate capacitor , with 10mm separation is charged to 100v, you then seperate the plates to 100mm, what voltage is on the plates now?Most people will jump straight in with 10v (the wrong answer BTW)A physical demonstration is much more fun. Take a grounded brass plate (or any avaliable grounded metal surface. Place a sheet of mylar on it (50 to 100um), Take another brass disk with a porcelain knob attached, place it on the mylar, charge it to 100v , lift it off the mylar (holding the knob), and touch iy against a colleague and watch him jump. (you can get around 20kV) This was a part tricky a century ago, the two brass plates were covered with dissimilar insulators, you would rub them together to get a decent potential then lift one off.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 05, 2016, 02:04:18 am
content: Re: Two charged spheres.(n.b. a condenser is the hot part of a refrigeration system, in historical contexts we still talk of "condensers" when Leyden Jars are relevant. But in a modern context, no-one says the "galvanic pile" in their laptop is going flat, if you want to use condensortivity to measure condensortive effects you need to be consistent and the units are milli-microfarad (we didn't have pico back then))The thing with the capacitance of charged spheres is that geometry and potential energy are intermixed with the whole arrangement. Also people mix up potential and potential difference. Coulombs law requires charge conservation, but if you move the pieces around you change the geometry, if you change geometry you change capacitance, if you change capacitance you change the voltage, you also need to add or remove mechanical energy when you change the capacitance of a charged system. Many of these science-fair demos rely on sleight of hand where the operator is changing geometry and or inputting/removing mechanical energy and you can't see this.The simplest demo is the pulling apart of capacitor plates, which has a counter-intuitive result, in this the geometry "increases" , but to do this you have to apply tension, and then you are adding energy to the system, hence the charge is constant, voltage goes up, electric field is constant, and energy stored in that field increases.I'm not sure in your example if the 1MV is between the two spheres, or the potential w.r.t earth (that makes a big difference!)But there are some things that happen,(a) as you open the big sphere some of the charge on the outside races around to the inside, so the voltage drops to 700kV??, the capacitance also increases. As soon as you pull the latch the two halves will fly open (repulsion of likes), so energy is removed from the system(b) when you put the little sphere inside you need to push it in (if opposite charge) or hold it back, so adding/removing energy.(c) with the sphere inside, there is much more inter-sphere capacitance, so the potential difference will be much less (if opposite charged)(d) at this point I think, if you short out the outer sphere, so it has zero voltage, but there will be still energy inside the sphere(e) if you then pull out the inner sphere (you need to add energy to this), magically there is now a voltage on both spheres!There all sorts of things you can do, but it's only magic if you ignore the geometry and energy transfer effects.(edit: some typos)

author: John Heath
author_rank: Frequent Contributor
timestamp: December 05, 2016, 02:59:26 am
content: Yes moving the spheres around changes the energy for a preferred coulomb position and the charge voltage. However if careful not to discharge the sphere then when returned to there original position the energy and voltage will be the same. This is why I said 1 M volt at 10 p farad to keep track of the energy. This being said a sphere within a sphere can be consider a condenser yes/ no. And as seen by the video the condenser can not be discharge when the small sphere is inside the big sphere. The same can be said of our sky charge at 100 volts per meter. It can not be measured or discharged as we are inside the voltage gradient. A resistor or copper wire 1 meter long facing up will measure 0 volts in a vacuum voltage gradient of 100 volts per meter. I see the copper disk in the Faraday paradox as the same in that the magnetic field has caused a voltage gradient in the copper disk but we can not measure in has one enters that voltage gradient when you try to measure the copper disk.there is a voltage gradient across a resistor and there is a voltage gradient in the vacuum that the resistor is in. The resistor gradient can be measured but not the vacuum voltage gradient. We feel gravity but this is because the ground stops us from falling . If falling the gravity gradient can not be measure as per the equivalence principle. In any event that is my 2 cents on the Faraday paradox.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 05, 2016, 03:50:07 am
content: It is possible to measure the earths atmospheric electric field , typically by the use of some form of rotating probe, for example two electrodes 100mm apart rotated about a horizontal axis will yield 10v pk AC signal in a E-field of 100v/m.The instrument is called a "field mill"http://a-tech.net/ElectricFieldMill/There are commercial E-field sensor systemshttps://www.campbellsci.com.au/electric-field-sensorfor example that provide alerts for an impending thunderstorm , or local corona activity (useful in areas with explosive dust hazards)

author: John Heath
author_rank: Frequent Contributor
timestamp: December 05, 2016, 12:37:03 pm
content: Interesting link. Thanks for posting. The wiki article is short. Maybe some googling can shed more light on an e field mill.

author: John Heath
author_rank: Frequent Contributor
timestamp: December 05, 2016, 12:46:50 pm
content: Found a nice video on its construction with more detail.