Consider the following thought experiment.

One end of a lamp is connected to one terminal of a power generator. The other end of the lamp is connected to the ground via a metal copper as follows. Assume that the generator is placed quite far above the ground.

enter image description here

Physics textbooks say that our earth is a giant capacitor that is greedy for electrons. It is also said that electric current flows if there is a closed circuit.


In this scenario, will the generator turn the lamp on?


I am not sure whether the generator should turn the lamp on or not.

  • If the generator turns on the lamp, there are electrons flowing from the generator to the earth. But how can the generator produce electrons from mechanical energy? It seems it violates the conservation of charges. So it should not turn the lamp on.

  • But borrowing an analogy of our electric outlet, if we touch the live (hot) wire without wearing high impedance shoes, we will get electric shock even there is no closed circuit (as far as I know).

enter image description here

  • $\begingroup$ Well, what do you think? $\endgroup$
    – Bob D
    Nov 28, 2021 at 17:12
  • $\begingroup$ @BobD: I am not sure. If the generator turn the lamp on, there are flowing electrons from the generator to the earth. But it does not make sense that the generator can produce electrons from mechanical energy of the wind. :-) $\endgroup$ Nov 28, 2021 at 17:16
  • $\begingroup$ Do you see a complete circuit here? $\endgroup$
    – Bob D
    Nov 28, 2021 at 17:26
  • $\begingroup$ @BobD: If we touch the live (hot) wire without wearing insulated shoes, we get electric shock, right? There is no closed circuit also (I think). $\endgroup$ Nov 28, 2021 at 17:30
  • $\begingroup$ I'm addressing your first bullet. How would the current to the lamp return to the 300 v generator? $\endgroup$
    – Bob D
    Nov 28, 2021 at 17:37

1 Answer 1


Here is what happens if the $300V$ wind generator tries to create a current in the wire.

enter image description here

At first some electrons will move e.g. to the right in the wire above.

However this leaves one end of the wire positively charged and the electrons are attracted back, within a short time the $300V$ would not be able to move any more electrons and the current stops.

So a closed circuit is necessary for a current to flow.


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