directional cables?

Simply-q: Current flow is indeed a flow of electrons. Electrons ARE the charge carriers, which is why we call this field "electronics" instead of "protonics" .... The measure of current is ultimately the measure of how many electrons pass a given point in a given amount of time. If you have 6.241 times 10 to the 18th electrons passing a given point in one second, you have one Ampere of current flowing.

Herman: As for current, it is indeed the flow of charge. It does not have to be electrons and slow drift speed is a reality as stated.

Both of these statements are correct, although Simply_q's statement is more narrow in context, applying to the specific situation of electricity propagating through a conductor.

Best regards,
-- Al

I thought my post yesterday reconciled the different points of view here, with two of the protagonists expressing agreement, and the other one not expressing any disagreement.

Guess I was wrong, although I don't quite understand why.

Best regards,
-- Al

Hi guys,

I think that in both this thread and the "speaker cable life span" thread a lot of the disagreement may be resulting from differing interpretations of the words "drift" and "flow."

If ac is applied to a cable, a given electron will "move" (aka "drift") an EXTREMELY small but non-zero distance during the first half-cycle of the waveform. During the second half-cycle of the waveform, it will move back to where it started. That movement will repeat for as long as the same signal is present.

On average, electrons at all points along a given conductor of the cable will do the same thing. The movement of electrons near the destination end of the cable will lag the movement of electrons near the driven end of the cable by a miniscule amount of time corresponding to the signal propagation velocity, which will be in the rough vicinity of 50 to 90% of the speed of light in a vacuum.

Although the individual electrons are moving back and forth across an infinitesimal distance, if we define a cross-section of the cable at any given point, and if ON AN RMS-AVERAGED BASIS, 6.241 x 10exp18 electrons move past that cross section in each second (in either direction), then 1 ampere of ac current is "flowing."

Meanwhile "charge" is conducted from one end of the cable to the other at near light speed, as I indicated. The charge is carried at the destination end of the cable by electrons that are not the same electrons as the ones near the source end of the cable, but which move similarly.

Agreed?

Best regards,
-- Al

Simply_q, could you clarify what you mean when you say that electrons drift under ac conditions?

Are you saying that they drift back and forth over a very short distance within the cable, as I indicated in my post yesterday? Meaning that a specific electron near the source end of the cable will never emerge from the other end of the cable (assuming there is no dc offset present)?

Or are you saying that they drift, to cite an example, all the way from the "hot" connection of the source component's output jack, through the cable and the input circuit of the destination component, then through the other leg of the cable to the ground connection of the source component's output jack, and then all the way back over that same route, but in the other direction, to the "hot" connection of the source component's output jack?

Or something else?

I think that clarification may help to break the impasse that this thread seems to have reached.

Best regards,
-- Al

Herman, I'm inspired to continue just a bit longer by this comment:

Almarg: Are you saying that they drift back and forth over a very short distance within the cable, as I indicated in my post yesterday? Meaning that a specific electron near the source end of the cable will never emerge from the other end of the cable (assuming there is no dc offset present)?

Simply_Q: Yes.

My point has been that whenever there is any current flow (in this particular context), there must be a net drift of electrons. It matters not that the drift may alternate direction over time. To say there is no drift is to say there is no current.

Simply_Q, my statement, to which you agreed, implies that there is no "net" drift, just a drift back and forth over some small distance, the location of which remains essentially unchanged for any given electron.

Can the word "net" be deleted from your statement without changing the meaning you intended? Is so, I think we are all in agreement. If not, then the impasse remains and I shall cease and desist.

Best regards,
-- Al

Simply-q: To understand why I use the term "net," you need to understand why I use it with the term "drift."

"Drift" is used to distinguish from "movement." With no current flowing there is still movement. The electrons in the wire are moving about randomly in all directions near their Fermi velocity. And at any given point, the number of electrons crossing in one direction will generally be the same as the number of electrons crossing in the opposite direction.

However if you apply an electric field, in addition to moving about at their Fermi velocity, the electrons will now take on a small velocity in the direction of the applied field. This is the drift velocity. And as a consequence, the number of electrons crossing that given point in one direction will now be greater than the number of electrons crossing in the opposite direction.

In other words, there is a net drift in that direction.

So, as long as there is current flowing, be it DC or AC, there will always be a net drift of electrons, because even if the direction of current changes alternately from one direction to the other, there will always be more electrons crossing that given point in one direction than the other.

Does this make it more clear where I'm coming from?

Yes, it does. That is an excellent explanation, and as far as I am concerned our positions are now converged.

Best regards,
-- Al