ELECTRON flow speed

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domnic

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Electrons travel about 5.2 miles in a wire that powers a motor ( ect ) ???????????????????????????????????????????
 
If you look at the number of electrons per second that constitutes 1 amp of current, and the total number of electrons in a copper wire, you will calculate a surprisingly low average electron speed.

Don't confuse this electron speed with the speed that an electric field propagates along a wire.

Jon
 
winnie said:
If you look at the number of electrons per second that constitutes 1 amp of current, and the total number of electrons in a copper wire, you will calculate a surprisingly low average electron speed.

Don't confuse this electron speed with the speed that an electric field propagates along a wire.

Jon
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Current is typically a difficult concept because of the way it is defined and measured, generally speaking it is defined to be the motion of charges, but meanings vary with context. To the physicist, the “electron current” model is used, where as to the engineer, the “dQ/dt” model is enough. Both of these models describe the current in different ways - one considers the electron velocities, density, and mean collisions over an average time interval, and the other as an expression of charge differential with respect to time.

Regardless of the context, these descriptions can obscure the motion of charges and may not specify whether it is one electron passing a surface at high velocities or many electrons passing through the surface at a lower velocity. To make matters more abstract, the motion of charge does not necessarily imply the motion of matter or charge carriers; charge is a proper of matter! So the time differential of charge is the rate at which the property of attraction/repulsion of matter is transferred from one body onto another, and the electron current expresses this with the intrinsic charge possessed by the carriers.

The worst part is that electron motion and charge are not actually measured when talking about current; The measurement of current is an indirect means of relating it back to charge, and as the SI Base Unit “Ampere” suggests, the REAL quantity observed/measured is the “action” or “force at a distance phenomena” from these so called charges in motion. Sure, charge has the unit Coulombs, but it is derived and explained by the Ampere, in turn correlated by FORCE!
 
domnic said:
Electrons travel about 5.2 miles in a wire that powers a motor ( ect ) ???????????????????????????????????????????
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In your example assuming an AC motor, average velocity is zero just as the average (DC) current is zero!

In a DC system it depends on the voltage (pressure). Obviously visually if you had a very thin wire fewer electrons would be involved so velocity is higher. They also don’t really “move”. The word we use is tunneling. They just sort of randomly teleport every so often. We look at the probability of an electron being in a particular location but that’s about it. In fact we don’t bother to measure or worry about electron velocity except within semiconductors and even then hole velocity is more useful and there are relatively simple formulas for that. The higher the doping the slower everything is. This creates a capacitance and is part of what limits microcircuit switching speeds.

So this is the problem. There is no specific fixed speed. You need to know the material including any contaminants or alloying down to the parts per billion level, the conductor geometry, and the applied voltage.

In a wire it is more useful to look at the flow of electrons per second, not their speeds. This is like measuring the flow in a river and not the speed. One ampere is one coulomb per second and one coulomb is 6.24x10^18 electrons per coulomb (Avagadros number). Electrons are pretty small so we use a large number of them in calculations.
 
I liken electron flow in a conductor to a hose filled with marbles:

Push a new marble in at one end, and one immediately pops out of the other end. It's not the same marble; that takes time. But the effect is instantaneous.

The real question is how far can a given electron propagate during one-half cycle, after which it reverses and moves the same distance in the other direction.

Added: As for a literal answer, I've seen about 1mm per second.
 
Given that electrons do not move in a conductor like vehicles on a road, and the electrons move back and forth constantly leaving this atom and joining that atom, the single electron could NEVER move 5.2 miles or it could eventually move 5.2 miles down the line.
It may take many years if everything’s lined up right…

Now, if your counting back and forth distance, that’s another thing..
 
Hv&Lv said:
Given that electrons do not move in a conductor like vehicles on a road, and the electrons move back and forth constantly leaving this atom and joining that atom, the single electron could NEVER move 5.2 miles or it could eventually move 5.2 miles down the line.
It may take many years if everything’s lined up right…

Now, if your counting back and forth distance, that’s another thing..
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I interpreted his statement to have meant 5.2 MPH because he was talking about speed, not distance. 5.2 miles of wire is a LONG circuit for a single motor...

There are a lot of opinions on the actual electron drift speed (as opposed to the CHARGE speed as winnie said). I've always used 1.2 inches per minute, (from some textbook years ago) which is 0.00113636 MPH.

5.2MPH is 5491.2 inches per minute. Nothing I have ever seen is anywhere close to that speed.
 
Jraef said:
5.2MPH is 5491.2 inches per minute. Nothing I have ever seen is anywhere close to that speed.
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Yes you have.

I know that it is old tech, but I am sure you've seen a cathode ray tube.

Of course we are no longer talking about electrons moving in a conductor :)

-Jon
 
Jraef said:
I interpreted his statement to have meant 5.2 MPH because he was talking about speed, not distance. 5.2 miles of wire is a LONG circuit for a single motor...

There are a lot of opinions on the actual electron drift speed (as opposed to the CHARGE speed as winnie said). I've always used 1.2 inches per minute, (from some textbook years ago) which is 0.00113636 MPH.

5.2MPH is 5491.2 inches per minute. Nothing I have ever seen is anywhere close to that speed.
Click to expand...
Oh…
I assumed we were talking drift speed possibilities. Didn’t think it was MPH.

mea culpah..
 
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