How Fast is elcectricity

Saiph · Mar 17, 2005

cent, the entire point is that the electrons don't have to travel the entire distance to transmit the electricity. See the water in the hose analogy above. Electricity travels much faster than the constituent electrons. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

pizzaguy · Mar 17, 2005

Electricity travels much faster than the constituent electrons. DAMN, another quote that should have come from me... <img src="/images/icons/crazy.gif" /> <div class="Discussion_UserSignature"> Note to Dr. Henry: The testosterone shots are working! </div>

Saiph · Mar 17, 2005

well, you've basically said it several times pg. Don't be so hard on yourself. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

pizzaguy · Mar 17, 2005

Yes, but you said it in few words and I could'nt seem to do that. (But then, perhaps, after all the blabbing in this thread - the point has been made and he understands basically what is being said.) <div class="Discussion_UserSignature"> Note to Dr. Henry: The testosterone shots are working! </div>

centsworth_II · Mar 17, 2005

"...the entire point is that the electrons don't have to travel the entire distance to transmit the electricity.... Electricity travels much faster than the constituent electrons." True, the question of electron speed crept into this thread on the speed of electricity. However, I think the two are confused in most peoples' minds -- as they were in mine until recently. I was frankly surprised at the relatively slow speed with which electrons move along an electric wire. Does the water hose analogy break down where speed of flow is concerned? When more force is put on the water, the flow through the hose is faster. Does the speed of electrons through a wire increase with added force (amps)? <div class="Discussion_UserSignature"> </div>

Saiph · Mar 17, 2005

when a higher voltage (the force) is applied, the drift velocity (flow rate) of the electrons increases accordingly. The electricity can be thought of as a wave through a medium, just like water waves or sound waves. The wave moves through the air or water, but the air and water molecules don't move much at all (often in a circle so there is no net motion). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

siarad · Mar 18, 2005

<blockquote>In reply to:<hr />siarad - Yes, please state your source for electron speed.<hr /></blockquote> I was not giving electron speed but electricity speed except saying holes transmit electricity more slowly than electrons & also in the opposite direction if you put an ammeter in. By electricity I was assuming information as it's a bit of a strange word to me.

siarad · Mar 18, 2005

Was it the great Maxwell who thought it was a wave outside the conductor & simply guided by it.

Saiph · Mar 18, 2005

holes should transmit it just as fast as electrons, as a "hole" is merely the absence of an electron. I've got a feeling a charge disparity should arise otherwise (i.e. the wire wouldn't remain neutral). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

siarad · Mar 19, 2005

I guess in a way you're right as Holes can't really occur in a wire where all transport is via electrons. Be assured Hole transport is much slower than electron transport & when holes are in an unwanted minority such slowness is a real pain to designers. The transport mechanism has to exist in the (semi)conductor you can't inject holes or electrons like water to expel them at the end, as you say the charge has to remain neutral, although you may see the word used. The lack of transport is called an insulator & other than tearing apart atomic bonds you can't inject electrons. As ever there's a problem with words having different meanings, understood by people who work with it as a concept not a definition. Realtime computing can't possibly be so as it takes time but is clear to workers using it, red-shift is nonsensical for radio waves but the concept implied if reasonable etc.

Saiph · Mar 19, 2005

a "hole" as I understand it is a positive charge in an area vacated by an electron. It is an area that the negative charge of the electrons no longer "shield" or fully negate. However, as the hole is caused by an absent electron, it should move the same way as far as I know. Feel free to point me to other resources though. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

yevaud · Mar 19, 2005

Ummm, holes in structure are important to superconductivity, as I remember the research in materials science. Not sure that's relevent here, but I thought I'd make mention of it. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

siarad · Mar 20, 2005

Ah I see your point of view now. A hole is not where an electron has been removed it is where one is missing i.e. it was never there. I hope you see the difference as electronic flow current is by free electrons who can travel anywhere within the interstices of the wire. Holes however are an orbital thing & don't exist as an entity so can't travel freely within a conductor which is why they move so slowly. In your way of thinking the current transport would still be electrons & would be from -ve to +ve whereas Hole transport is from +ve to -ve as can be shown with an ammeter. Holes can't exist in a wire but are manufactured by a crystalline structure i.e. a semi conductor. Sorry I'm rushed so can't give an entire treatise.

Saiph · Mar 20, 2005

right, however a hole "moves" when an neighboring electron fills in the hole, and leaves another behind it. So in a semi-conducter, electrons and holes must move at the same speed through that material. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Mar 20, 2005

Siarad - Ok, if you were talking about electricity and not electron speed, I still am curious about the source of 10% the speed of light. How did that get calculated?

spaceman186000mps · Mar 21, 2005

OK lol So I go to home depot and purchase 7,497,600 one hundred feet long drop cords and hook them all together stretched from the Earth to the Moon. Now ! I stand on the moon (In my spacesuit) with a lamp plugged into my approx. 240 thousand mile drop cord. You stand on Earth and plug your male end into a receptacle. How long before the bulb in the lamp lights up? Of course I realize You can't have a drop cord that long. It's only a thought experiment, not reality. <div class="Discussion_UserSignature"> 70 percent of novel proceeds www.trafford.com/06-1593 are donated to www.caringbridge.org </div>

pizzaguy · Mar 21, 2005

So I go to home depot and purchase 7,497,600 one hundred feet long drop cords and hook them all together stretched from the Earth to the Moon. Now ! I stand on the moon (In my spacesuit) with a lamp plugged into my approx. 240 thousand mile drop cord. You stand on Earth and plug your male end into a receptacle. How long before the bulb in the lamp lights up? Of course I realize You can't have a drop cord that long. It's only a thought experiment, not reality. First of all, with the voltage drop, the light would never come on, the cord's resistance would be too high!!! Anyway, here's an email I sent off to an engineering friend earlier today: ET: Happy Monday! Got a good one for you: If I ran an extension cord to the moon, 250,000 miles - how long after plugging it in would a light at the other end light? (Le'ts ignore the voltage drop, etc.) I say the velocity factor would be around .95 of free space - so about 1.5 seconds. What do ya think? Makr And here is his response: Well Markr..... If we uses 250,000 miles as the distance to the moon. That is 402,336 km or 402,336,000 meters. The speed of light is 299,792,458 m/s Fudge in a velocity factor for the cord of .95 and the corrected velocity of light is 284,802,835 m/s Distance divided by velocity equals time so the light comes on 1.413 seconds after the cord gets plugged in. But the observer on earth does not see the light come on until another 1.342 second later as the light travels back to earth. Total estimated round trip 2.755 seconds. Actually..... The moon travels around Earth in an elliptical orbit, with the Earth at one of the two focuses of the ellipse. As a result the distance to the moon vari <div class="Discussion_UserSignature"> Note to Dr. Henry: The testosterone shots are working! </div>

spaceman186000mps · Mar 21, 2005

So I go to home depot and purchase 7,497,600 one hundred feet long drop cords and hook them all together stretched from the Earth to the Moon. lol I think my calculator blew a whoopee So each mile of drop cord would require 52.8 , 100 feet long drop cords to stretch one mile or 5280 feet. now... 52.8 x 250,000 miles equals 13,200,000 or in other words it would take 13 million two hundred thousand, 100 feet long drop cords to reach the moon at 250 thousand miles distance. Now in pizza's that are exactly 12 inches in diameter touching side to side it would take 1,320,000,000 or one billion three hundred and twenty million pizza's... lol I could eat a few right now. ok... with all that said, I feel like I must roll the first pizza 360 degrees full circle and see how long it takes the last pizza on the moon to roll That is, if i don't eat a few in the middle along the way. But seriously Distance divided by velocity equals time so the light comes on 1.413 seconds after the cord gets plugged in. But the observer on earth does not see the light come on until another 1.342 second later as the light travels back to earth. Total estimated round trip 2.755 seconds. 1.413 subtract 1.342 means the electrons or pizza's took .071 thousandth of a second longer to travel to the moon through the drop cord than the visible light bulb waves or particles took to to be seen visually from earth. very interesting indeed. <div class="Discussion_UserSignature"> 70 percent of novel proceeds www.trafford.com/06-1593 are donated to www.caringbridge.org </div>

siarad · Mar 22, 2005

Sorry my words are inadequate, it's why I took up electronics more than half a century ago, nice pictures & graphs I could understand & draw. Electron conduction is by 'free' electrons able to move in any direction, holes can only move by coincident orbits a much rarer occurrence. Electrons are not the means of conduction in this instance as I pointed out by the reversal of an ammeter showing the direction of current. There can be both forms of conduction in a single semi-conductor referred to as majority & minority carriers. Free electrons are alone in orbit so can can leave it to travel freely but the ones taking part in hole conduction can't & can be part of an unbreakable orbit normally an insulator.

siarad · Mar 22, 2005

Next time you're speaking on the phone you can talk over the one wire simultaneously without interaction. Trust me do try it. <img src="/images/icons/wink.gif" /> Why do you think digital & analogue transmission are different look up Fourier analysis. OK there is a big difference, digital takes 10 times the bandwidth. <img src="/images/icons/laugh.gif" />

siarad · Mar 22, 2005

I measured it, it takes about 10ns per foot which is very problematical & why more & more has to be packed into IC. Even then delays are a problem especially the variance due to data in busses necessitating clock circuitry to re-time, itself slowing the circuitry. This data-speed variance & crosstalk is why parallel busses are limited & why PC are going over to less speed & time limited serial HDD & busses. When we used to tape-up PCB we had to calculate the speed using Maxwell's formula regarding permittivity & permeability substituting the 'relative' values for the items used but it's all done by my PC now. velocity(light)^2 = 1/ (permittivity * permeability) The speed of electricity is not easily defined & I did give an example where you can see the difference on your TV screen, it's like asking how long is a piece of string.

siarad · Mar 22, 2005

<blockquote>In reply to:<hr />Fudge in a velocity factor for the cord of .95 and the corrected velocity of light is 284,802,835 m/s <hr /></blockquote> I very much doubt that figure just look at Maxwell's formula: inductance = length * permeability velocity(light)^2 = 1/ (permittivity * permeability) The inductance would be huge with that length & the initial electricity would appear over a time if you look at Fourier analysis. Fibre optics are used to overcome the slowness & wavefront distortion of electricity over long lengths.

Saiph · Mar 22, 2005

ahh, now I see what you're saying. I forgot there is a distinction between standard electron conduction and semi-conductor holes. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

pizzaguy · Mar 23, 2005

inductance = length * permeability Where did you get THAT? How can someone determine inductance without taking into consideration the DIAMETER of the wire? (And no where can I find permeability in the formulas for a straight wire.) I will admit to never really thinking about the inductance of a straight wire very often, but came up with two formulas for calculating it. The first: L = 2*l*(log(4*l/d)-3/4) (nH/m) (1) where, L = inductance of lead wire (nH/m) d = diameter of lead wire (cm) l = length of lead wire (cm) The second comes from Tim Healy, Santa Clara University: "Surprisingly, it is not easy to find an expression for the inductance of a straight piece of wire, and it is far more difficult to find out how that expression was obtained. And yet this result is very useful as a building block for more complex structures, and also because the inductance of a wire is important in high frequency or high speed electrical circuits." The total low frequency inductance (internal plus external) of a straight wire is: Ldc = 2L[ln(2L/r) - 0.75]nH where Ldc is the "low-frequency" or DC inductance in nanohenries (nH), L is the length of the wire in cm, and r is the radius of the wire in cm. This result is based on the assumption that the radius r is much less than the length L, which is commonly true. For sufficiently high frequencies skin effects cause the internal inductance to go to zero and the inductance becomes: Lac = 2L[ln(2L/r) - 1.00] E.B. Rosa, "The Self and Mutual Inductances of Linear Conductors", Bulletin of the Bureau of Standards, Vol.4, No.2, 1908, Page 301ff. But even then, if you are gonna make a big deal out of the inductance, fine. Bettter take into consideration that th <div class="Discussion_UserSignature"> Note to Dr. Henry: The testosterone shots are working! </div>

seppstefano · Jun 8, 2006

Hi all, sorry for resuming such an old thread. I found as very interesting the formulas for evaluating L of a single wire. Any idea of the threshold frequency between so called DC and AC freq? Kind regards, Stefano

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