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?
Best Answer
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.