The speed of electricity?

[Soapy Sam]

Simple question. What actually is the speed of electricity in a wire?
Specifically a phone call in a standard twisted pair copper wire?


I'm mildly curious about how far an electronic bank transfer actually could have gone in the five days it is predicted to take.

(It will be required to cover about 500miles, which I think is just about within the capabilities of the Pony Express).

Lets call it 100 hours. 360,000 seconds.

[69dodge]

over half the speed of light

http://www.faqs.org/faqs/LANs/ethernet-faq/

[Soapy Sam]

[3.11] What is propagation delay?
The propagation speed of a medium refers to the speed that the data travels through that medium. Propagation delays differ between mediums, which affect the maximum possible length of the Ethernet topology running on that medium.

In the following table, c refers to the speed of light in a vacuum, or 300,000 kilometers per second.

Medium Propagation Speed
------ -----------------
Thick Coax .77c (231,000 km/sec)
Thin Coax .65c (195,000 km/sec)
Twisted Pair .59c (177,000 km/sec)
Fiber .66c (198,000 km/sec)
AUI Cable .65c (195,000 km/sec)



Muchas Gracias!


ETA- I reckon that's about eleven times the distance to Pluto in 100 hours.

[The Don]

Most banking systems run a nightly batch to fully post transactions.

As a result 24 hrs to process a bank transfer would not be unreasonable, 5 days would

[Soapy Sam]

Don- As you'll know, this weekend is a holiday in Glagow, so some delay might be expected.

But this transfer originates in Jersey.

Also. Two transfers have been made. (We're talking BOSH here). One transfer was handled by telephone and went through inside four hours. The other, by internet banking, is not expected to clear before Monday.

I do wonder where that money is sitting between yesterday and then...

[TeaBag420]

Originally posted by The Don
Most banking systems run a nightly batch to fully post transactions.

...
I run one, too, but it has nothing to do with transactions.

Soapy, your bank's Cash Management Specialist should be able to give you a report of exactly when your money hit various points along the way.

[Soapy Sam]

Gratifyingly, the dosh has aleady arrived. (In under 24 hours). I can only suppose the warning about it taking till Monday erred somewhat on the pessimistic side. This is a bank holiday weekend, I suspect they put warnings everywhere.

Anyway. I have acquired a fact which will doubtless come in handy in a pub one night.

[mummymonkey]

Originally posted by Soapy Sam
Anyway. I have acquired a fact which will doubtless come in handy in a pub one night. Can you let us know where you drink Soapy? Just in case.

[phildonnia]

Bear in mind that the actual charge carriers in a wire move very slowly, on the order of inches per hour.

[rwguinn]

Originally posted by phildonnia
Bear in mind that the actual charge carriers in a wire move very slowly, on the order of inches per hour.
Now I know that can't be right.
Charges are wired to my bank at about Warp 7.
Credit carriers, however...
What was the speed of snails?

[Diogenes]

More than you probably wanted to know..

http://www.amasci.com/miscon/speed.html


The author estimates the speed of current in a lamp is about 8.4 cm/hour ...



Oh, the five day wire transfer thing. Thats just CYA.. If you read the fine print, it probably says they are not responsible if it never gets there...

[Just thinking]

Originally posted by rwguinn
Now I know that can't be right.

Oh, but it is!

Consider, if you will, a long hose filled with water attached to a faucet at one end and open at the other. The moment you turn on the faucet the water begins to flow out the open end -- but it is not the water that just entered the hose from the faucet. What happened is that a pressure wave traveled through the hose much faster than the water and resulted in water flowing out the open end. (It was simply pushed out.) The same is true for electrons in wire -- what happens is that the charge signal travels much much faster than the electrons themselves and results in a voltage potential at the other end of the wire -- this potential then allows electrons at that far end to now do work. It is the speed of that voltage potential, not the electrons, that approaches the speed of light.

[Ziggurat]

Originally posted by Just thinking
Oh, but it is!

I think it was a joke. I don't think he was talking about electrons or copper when he said: "Charges are wired to my bank at about Warp 7."

But yes, your technical summary is quite correct.

[Just thinking]

Originally posted by Ziggurat
I think it was a joke.

You may be right -- but I have found that many people are quite surprised to find out just how slow electrons actually travel through wire.

[TeaBag420]

Originally posted by Just thinking
You may be right -- but I have found that many people are quite surprised to find out just how slow electrons actually travel through wire.

How DO slow electrons actually travel through a wire?

[Just thinking]

Originally posted by TeaBag420
How DO slow electrons actually travel through a wire?

Is this in reply to my not using the adverb slowly when I instead quickly typed just slow ... or do you actually want a brief description of electon movement in wire across some potential?

Really, TB, there are quite a few entries in these threads that use (or should I say abuse) the English language far worse than an occasional slip as seen in my oversight.

[Bruce]

Originally posted by TeaBag420
How DO slow electrons actually travel through a wire?

I was going to ask the same thing. As I understand it, the electrons only travel across the valence shells on the outer surface of the wire (the metal part). Electrons can't travel through a wire because there are no empty valence shells for the electrons to hop along.

How was the speed of the electrons confirmed experimentally? I've never heard of a way to distinguish one electron from another.

What's the difference between charge build-up and electron build-up?

These are the reasons why I have such trouble understanding electro-chemistry. :(

[TeaBag420]

Originally posted by Bruce
I was going to ask the same thing. As I understand it, the electrons only travel across the valence shells on the outer surface of the wire (the metal part). Electrons can't travel through a wire because there are no empty valence shells for the electrons to hop along.

How was the speed of the electrons confirmed experimentally? I've never heard of a way to distinguish one electron from another.

What's the difference between charge build-up and electron build-up?

These are the reasons why I have such trouble understanding electro-chemistry. :(
And the "outer surface" (redundant, by the way) is different from the wire how?

Otherwise I think you're asking great questions.

[Bruce]

Originally posted by TeaBag420
And the "outer surface" (redundant, by the way) is different from the wire how?


The valence shells of the atoms within the lattice are filled by the electrons of adjacent atoms. Only the outermost atoms of the lattice have empty valence shells that can pass the charge. This site explains it fairly well:

http://www.schoolscience.co.uk/content/5/chemistry/steel/steelch1pg1.html

I find that the concepts of electricity and it's mechanics varies broadly among physicists, chemists, and engineers. I've done my best to learn from each discipline, and I'm still terribley confused.
:(

[jj]

Speed of an electron.

Let's take a piece of wire that is 1 mole of wire. Make it copper. Copper has 1 conduction electron. That means that there are 6.02 x 10^23 electrons in this mole of copper.

That bit of wire would make a decent cable a few feet long, at most.

If we moved 1 amp through it, that would be a bit more than 10^19th electrons/second.

Consider, then, the current we'd see to have the drift velocity in this wire be 1 foot/second. It would be on the order of 5x10^4 amps. The wire would melt.

I'd be more exact but my calculator is upstairs.

[Just thinking]

Originally posted by Bruce
How was the speed of the electrons confirmed experimentally? I've never heard of a way to distinguish one electron from another.

It's been a while since I did the whole "Drift Velocity" thing, but perhaps this page (http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html) can give a general description of what's going on.

[Just thinking]

Originally posted by Bruce
The valence shells of the atoms within the lattice are filled by the electrons of adjacent atoms. Only the outermost atoms of the lattice have empty valence shells that can pass the charge.

Your link states ... The outermost, bonding electrons are no longer bound to individual atoms. They are spread randomly through the lattice. They form a ‘cloud’ of electrons which are free to move through the solid. The electrons behave like a gas that is confined by the edges of the piece of metal.

This clearly states that electrons move through the entire wire, not just along the surface of it. It says "by the edges", not "to the edges".

[Art Vandelay]

Originally posted by Just thinking
Really, TB, there are quite a few entries in these threads that use (or should I say abuse) the English language far worse than an occasional slip as seen in my oversight. While I normally find his nitpicks annoying, at least this one evidences cleverness and a sense of humor. Sort of like
"Call me a cab."
"Okay, you're a cab."

BruceOnly the outermost atoms of the lattice have empty valence shells that can pass the charge.If that were true, shouldn't resistance depend on the cross-sectional perimeter, rather than area?

TeaBag420And the "outer surface" (redundant, by the way) is different from the wire how?It is possible to have an inner surface. A balloon, for instance, has one.

[Bruce]

Ugh. Picky, picky, picky. :D

Engineers and physicists like to use the "waterfall" analogy to describe the flow of electrons in a direct current. The height of the waterfall represents potential (voltage), and the flow of the water represents current.

This analogy totally falls apart when describing alternating current (AC).

"Well, uh, imagine that the river flows backwards and forwards at different frequencies."

Ok, smarties. Explain the speed of electricity in AC. :p

[Bruce]

Originally posted by Just thinking
Your link states ... The outermost, bonding electrons are no longer bound to individual atoms. They are spread randomly through the lattice. They form a ‘cloud’ of electrons which are free to move through the solid. The electrons behave like a gas that is confined by the edges of the piece of metal.

This clearly states that electrons move through the entire wire, not just along the surface of it. It says "by the edges", not "to the edges".

True, the electrons are delocalized and free to move about, but the flow of electrons will favor the path of least resistance, which is around the lattice, not through it.

It's like when someone pours water over your head. The water flows around your body. I suppose you could say that a few molecules of water are absorbed by your body, and a few molecules of water within you body leave and become part of the flow, but that's not the same as saying the water being poured over your head travels through your body.

[El Greco]

The way I see it it's like a train. You push the last car of the train and you almost immediately see the first car move. AC is not any different, you just push/pull the last car.

In each car there are electrons wich move very fast, almost at the speed of light. But that movement is scattered and they remain in the boundaries of the car, so they only move forward at a very slow speed.

If you remove the quantization of the train/car example, I think this is a pretty accurate analogy.

[Just thinking]

Originally posted by Bruce
Engineers and physicists like to use the "waterfall" analogy to describe the flow of electrons in a direct current. The height of the waterfall represents potential (voltage), and the flow of the water represents current.

This analogy totally falls apart when describing alternating current (AC).

Well, that's not very hard to do -- but you don't use a waterfall. The waterfall is used to represent a battery, which is usually a DC device (many things in electricity use analogies with water, and each has its specific application -- that's why the waterfall doesn't work with AC). If you want to represent a source of potential for AC, try using a piston in a cylinder that has a hose (or tube) of the same diameter connected at one end (filled with water) and is configured to reconnect back to the other side of the cylinder with the piston; this will allow it (the piston) to move freely in each direction. (No water should pass by the piston in the cylinder.) The rate it moves back and forth represents the frequency and the length of each stroke can represent the potential (voltage).

[Just thinking]

Actually, what is stated above is not quite correct -- the waterfall is not the battery, the waterfall represents whatever device is consuming power and thus lowering the potential of the moving electrons (e.g.; light bulb, motor, etc.). The battery would be whatever device tansports the water back up to the level of the top of the waterfall. But the waterfall does only work in a DC application, just as some devices only work with DC circuits (DC solenoids, DC motors, etc.). For a device that works in my AC analogy using a piston, simply consider a second piston (somewhere down the hose) with a lever handle pivoting from the center of it going through the hose (with a watertight seal) that can move back and forth from a fixed pivot point outside. This 'handle' (extended beyond the fixed pivot point) can then be connected to any number of various devices which can then do work. Its back and forth motion can be used as-is or configured like the drive wheels on a steam locomotive to produce constant linear motion in one direction.

[TeaBag420]

Originally posted by Art Vandelay
While I normally find his nitpicks annoying, at least this one evidences cleverness and a sense of humor. Sort of like
"Call me a cab."
"Okay, you're a cab."

BruceIf that were true, shouldn't resistance depend on the cross-sectional perimeter, rather than area?

TeaBag420It is possible to have an inner surface. A balloon, for instance, has one.

Ah, a wire is actually a hollow tube. Gotcha.

[Just thinking]

Originally posted by Bruce
True, the electrons are delocalized and free to move about, but the flow of electrons will favor the path of least resistance, which is around the lattice, not through it.

This is only true for very high frequencies -- I believe in the mega-hertz range. Normal AC (50 or 60 Hz) is way too low for this skin-effect to have any real consequence. Electrons are just as 'happy' moving through copper wire as they are along its surface. (Did you get that, TB? "Happy Electrons" -- it's a new quantum state, like charm, spin, etc. Now we have Happy and Sad.)

[Art Vandelay]

Originally posted by Bruce
This analogy totally falls apart when describing alternating current (AC).

"Well, uh, imagine that the river flows backwards and forwards at different frequencies."

Ok, smarties. Explain the speed of electricity in AC. What if there are waves traveling along the river?

True, the electrons are delocalized and free to move about, but the flow of electrons will favor the path of least resistance, which is around the lattice, not through it."Favor" and "use exclusively" are not the same things.

[Bruce]

Originally posted by Art Vandelay
What if there are waves traveling along the river?


Nope. Not the same, because the current literally switches directions. 1 Hz means that the potential has completed one sine wave, meaning that it went positive, then negative, and back again. The current does the same thing.

[Just thinking]

Originally posted by Bruce
Ok, smarties. Explain the speed of electricity in AC.

Ah ... did you gloss over my piston analogy?

If you want to represent a source of potential for AC, try using a piston in a cylinder that has a hose (or tube) of the same diameter connected at one end (filled with water) and is configured to reconnect back to the other side of the cylinder with the piston; this will allow it (the piston) to move freely in each direction. (No water should pass by the piston in the cylinder.) The rate it moves back and forth represents the frequency and the length of each stroke can represent the potential (voltage).

The actual velocity of electrons behave as they do for DC in each half cycle -- but potential (voltage) is constantly changing, so you should look at a given instant to determine velocity.

[Bruce]

Originally posted by Just thinking

If you want to represent a source of potential for AC, try using a piston in a cylinder that has a hose (or tube) of the same diameter connected at one end (filled with water) and is configured to reconnect back to the other side of the cylinder with the piston; this will allow it (the piston) to move freely in each direction. (No water should pass by the piston in the cylinder.) The rate it moves back and forth represents the frequency and the length of each stroke can represent the potential (voltage).

I'm having a little trouble visualizing this. Can you make a drawing? It's sounds good.

Originally posted by Just thinking
The actual velocity of electrons behave as they do for DC in each half cycle -- but potential (voltage) is constantly changing, so you should look at a given instant to determine velocity.

Good.

This something that took me a long time to understand about AC. After studying DC, I had assumed electrons had to flow in one direction for an electric current to work. It didn't make sense to me that you could have electrons moving back and forth, but still have a working electric current. Turns out the electrons only need to be in motion, whether it be a continuous flow or in oscillation, to get "work" from an electric current.

The question in the OP was "What is the speed of electricity?" You normally think of speed as the distance something travels over time. For example, a light year is the distance light travels in one year. However, when discussing AC, the net distance an electron travels in one oscillation is zero (I think). As JT said, the velocity in this case depends on the instant within the oscillation.

As we've debated so far, even in DC, the speed of electricity depends on several things, including your definition of "electricity". Are you speaking of the average speed of the electrons, or the speed of an individual electron, the speed of a lightning bolt (electric ark), the speed at which information is transmitted through a wire, etc. All of these situations are completely different.

The speed of electricity is not a constant like the speed of light.

[Just thinking]

Bruce -- I'm not going to re-post all of what you just said, it would take up too much room and might get confusing, so I'll simply address the key points you made.

Unfortunately I don't have a drawing to quickly put up which describes my analogy (just yet -- I'll try making one), so re-reading my description a few times might help.

You are correct in that it is the motion of electrons that allows work to be done -- but don't be fooled into thinking that one type works for all examples. There are devices that require DC and cannot work with AC -- and vice-versa. (All the musical signals that come out of an amplifier to a loudspeaker are AC -- the automatic door locks in a car are DC and would just vibrate in place with AC.)

You are also correct in that the term 'speed of electricity' can mean several things, which is why it is seldom used in electronics texts. Usually what are important are the rates in which an electronic signal travels through a medium (such as wire) and the actual drift velocity of charge carriers (usually electrons). And of the two, it is the velocity of electronic signal that is referred to 99% of the time.

Is this of any help?

[Bruce]

Originally posted by Just thinking
I'm not going to re-post all of what you just said, it would take up too much room and might get confusing

:p

[TeaBag420]

Originally posted by Just thinking
This is only true for very high frequencies -- I believe in the mega-hertz range. Normal AC (50 or 60 Hz) is way too low for this skin-effect to have any real consequence. Electrons are just as 'happy' moving through copper wire as they are along its surface. (Did you get that, TB?

Yes, I did. Did you get that that was my original point?

[Just thinking]

Originally posted by Bruce
:p

I'm tellin' ya ... I get no respect!

[Soapy Sam]

I just learned my bank actually uses carrier pigeons...
Anyone know the airspeed of a pigeon?

[Bruce]

Originally posted by Soapy Sam
I just learned my bank actually uses carrier pigeons...
Anyone know the airspeed of a pigeon?

African or European?

[Bruce]

Smoke signals are much faster. Anyone know the speed of smoke?

[TeaBag420]

Originally posted by Bruce
I'm having a little trouble visualizing this. Can you make a drawing? It's sounds good.



Good.

...
The speed of electricity is not a constant like the speed of light.

Neither is the speed of light.

[Art Vandelay]

Originally posted by Bruce
Nope. Not the same, because the current literally switches directions.
So does the water. Sometimes it's going up, sometimes it's going down.

Just ThinkingYou are correct in that it is the motion of electrons that allows work to be done -- but don't be fooled into thinking that one type works for all examples. There are devices that require DC and cannot work with AC -- and vice-versa. Technically, it's not the motion of the electrons that does work, but the electric field. Of course, it's difficult to create an electric field without moving electrons. But just moving electrons around doesn't do work; there has to be some potential supplying work. And from a physics point of view, an electric field does work in almost all devices; it just doesn't do useful work. Shorting out and setting your carpet on fire, for instance, would fulfill the physics definition of "work".

[Bruce]

Originally posted by TeaBag420
Neither is the speed of light.

You can pretend it is. :D