Can electrons flow in opposite directions on the same wire, see schematic!

[poynt99]

Not at all.
As the motors do not draw the same current at each moment of time during each turn, due to the switching connections and the variable coupling between coils and magnets, it is obvious that there is an AC current (with a frequency depending on the number of turns/s and on the number of coils, + harmonics).

Yes this is true, however this is not the question of the topic. The question is not whether a current can flow in the common (because I have shown that it can under certain conditions), but whether it has to based on the notion that it appears to be the path of least resistance.

The issue has very little to do with which path has the least resistance, and quite a lot to do with Kirchoff's current law, and mesh currents. The only thing that determines if there is current in the common lead is if the loads are unbalanced or balanced. With a perfectly balanced load, the common lead can be removed and the circuit will operate the same. There will be no potential at the common node where the loads connect, and therefore no current in the common leg.

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[angryScientist]

With high frequency ac the current can flow in two directions at the same time. It's a well known fact in some circles. I'm thinking a transmission line that is long (longer than 1/2 wave length) or if the frequency is very high (since I just read a book on it). In one part of the wire the current is going one way and in another part the current is going another.

What really puzzles me is when you have a transmission line or antenna and the wave is reflected off the end and it comes back and is supper imposed over the next wave traveling in the opposite direction. At that instant it there would be no voltage on the line and no magnetic field surrounding it.

How in the world does the wave know to continue?! There is no difference in potential. It's like it just bleeps out of existence and then comes right back. There wouldn't be any momentum because the electrons would be standing still.

I still don't get it. It seems kind of freaky to me!

[poynt99]

If the frequency is high enough, then you could have an AC current on the skin of the wire and a DC current in the entire cross-section, including the skin.

It still comes down to the net potential across the wire, and for one half of the AC cycle the AC and DC currents will add, and in the other half they will subtract. The two currents are not mutually exclusive of one another (i.e. electrons never pass each other going opposite directions).

So there are not two currents running in opposite directions. The current will run either one way or the other, depending on the net potential across the ends of the wire at any instant of time.

Take as an example two current sources connected to a wire: one sources 10mA DC, and the other sources 1mA AC sine-wave at 500MHz. Now if you utilize your 10GHz Hall effect current probe (good luck finding one) to measure the current in that single wire, you will see a current fluctuating between 9mA and 11mA at a sine frequency of 500MHz.

.99

[poynt99]

What really puzzles me is when you have a transmission line or antenna and the wave is reflected off the end and it comes back and is supper imposed over the next wave traveling in the opposite direction. At that instant it there would be no voltage on the line and no magnetic field surrounding it.

That depends on whether the reflection is the same (open circuit) or opposite (short circuit) polarity as the incoming wave or pulse.

How in the world does the wave know to continue?! There is no difference in potential. It's like it just bleeps out of existence and then comes right back. There wouldn't be any momentum because the electrons would be standing still.

I still don't get it. It seems kind of freaky to me!

Transmission lines (TL) exhibit a local effect. A pulse sufficiently short to be small in comparison to the length of the transmission line will propagate along at some fraction of c, but until that pulse reaches the end, the "end" is not even aware of the pulse. If the end is not terminated in the characteristic Z of the TL, there will be a reflection, and if there are sequential pulses, the reflected pulse will intersect the next advancing one. What happens there is the same as what happens on a single wire; the two currents mesh. Either they add or subtract locally. They continue to propagate past each other because the TL is made up of a series of storage elements, and the energy in them can not be destroyed.

.99

[angryScientist]

First half, poignant. It's what I've read. I like. For sure.

Second, I'm still not seeing it. If they add together and nullify each other then where is the energy. Which dimension is the energy contained in? Not in the electric or magnetic or even mass.

I still don't comprehend...