The path of electrons in AC circuit?

Question

I have a question regarding the AC circuit shown below. If we ignore the voltage drop caused by the long cable, I think the device will work and the circuit can be considered as a closed circuit.

Now I am wondering about how the electrons can return back to the source to form a closed path and so a closed circuit!?

As it appears, there are 1000 of Kilometers between GND1 and GND2, or we can say that there is infinite value of ohms (resistance) between the two grounds. So, where is the closed path for the electrons flowing?

Answer 1

While it's common practice on schematics for small (i.e., all in the same place) circuits to show grounds that don't appear to be connected, this is just a convenient way not to clutter up the diagram with all the return paths.

If however you're talking about literally kilometers of physical ground, you'll find that in practice, at least with power delivery, there is always (afaik) a return conductor to ensure a low impedance to complete the circuit. In effect, this return conductor is in parallel with whatever conductance the actual earth connections afford, so some of the current will actually travel through the earth, but mostly it's going to be found in the wire.

RF applications might get away without this return wire, but then RF applications can oft times get away without either wire, so I'll leave that aspect for someone else to tackle, should you be interested.

Answer 2

Indeed, there isn't (assumed that the resistance between the two GNDs is infinite) and there is no closed circuit.

If the potentials are different, there may be an electrostatic discharge when the one with lower absolute potential will try to take charge from the other (giving electrons), but no continuous flow of current will occur.

Answer 3

Earth is actually conductive, even over long distances. A geologist can probably explain this better than I, but my understanding is that wet soil is chock-full of minerals and various salts. This makes it conductive.

Rural power delivery is often done with a single live conductor strung on poles, with the return path being two or more long grounds rods driven deep into the soil. This has lead to some unfortunate problems involving farms with livestock. I was aware of this when I was a kid many years ago and it is well documented. Do a Google search for "livestock stray voltage".

Modern power delivery methods now include the return conductor. That wasn't the case many years ago.

Answer 4

There is a thing called single wire earth return (SWER) common in HVDC systems. You can actually use the earth as a return path , but I still can't make out how the electrons flow. I don't think that there is an actual way for an electron to travel 100km and find its way from one electrode to the other. Research on internet was fruitless..

Answer 5

The general mass of earth is zero ohms but it is the connection to earth that adds resistance to the circuit. As pointed out in Australia there is a high voltage network called single wire earth return and it uses a single wire to a transformer and uses the earth to complete the circuit.