I have a question about what happens in following experiment: Assume we have a battery with two Galvanic half cell, eg. a magnesium anode and a copper cathode. Since copper has higher electrode potential that magnesium, the electrode with magnesium oxidizes and therefore becomes the negative terminal und the electrode with copper reduces and becomes positive terminal.

I want to find out what happens at the moment when we connect the earth only to the negative terminal, leaving the positive terminal disconnected? Does there happen a very short electrostatic discharge immediately after connection such that the electrons sitting in the magnesium chunk get absorbed by the earth?
(the earth is here considered as electrostatically neutral uncharged source with constant potential, which can absorb und donate a huge amount of electrons without changing it's potential) See also this image:

enter image description here

Question: What happens at the moment we connect the negative terminal (magnesium) having excess of electrons with earth und leave simultaneously the positive terminal unconnected?

Clearly, since the positive terminal is unconnected, there cannot establish a steady current because there is no closed circuit between positive and negative terminals. Therefore such connection will surely not drain completely the battery, but the question is if it could happen that only the burst of electrons which actually inhabiting the magnesium anode going be absorbed by the earth and then everything stops.

But I'm primary interested in electrostatic effects and want to know if there happens a electrostatic discharge at the contact moment within a very very short moment sending the excess electrons from negative terminal to earth or does there really literally 'nothing' happen?

Why I conjecture that such elecrostatic discharge should happen. At the moment when we connect the earth to the magnesium electrode seemingly the unconnected copper electrode isn't noticed by the system earth-magnesium electrode since we assumed that there is no connection to the copper electrode:

enter image description here

And since the earth is neatrally charged and the magnesium electrode contains a lot of electrons on it, it seems reasonable that all this electrons 'want' to run into the neutral earth at the moment we connect the earth to the magnesium electrode. Does it sound reasonable.

That seems to be quite similar to the question what happens immediately after we connect the positive to negative terminals of two Galvanic half cells but remove the salt bridge:

enter image description here

Again, clearly without salt bridge there can no consistent current happen because the salt bridge closes the circuit as ion conductor.

But nevertheless, at the moment we connect the two terminals/electrods whith a wire, shouldn't the excessed electrons at magnesium electrode not nevertheless flow to copper electode and then stay there to compensate the charge/potential difference? And only then because due to lack of salt bridge everything stops?

Are my reasonings correct or if not what is my error? (I asked the same question in physicsstack


2 Answers 2


Conncting two objects together, like earth and your circuit, in a way that does not close a loop will pretty much do nothing after connecting them.

When you connect two objects together, they will be at the same potential. If they originally were not at equal potential, it means that there was charge between them, and connecting the wire will discharge the potential difference quite rapidly as charges redistribute.

There will be no electrons or current flowing after that.

In order to have a flow of current, you need a loop with a potential difference.

Same way, a lamp lights up if you connect it to the both terminals of a say 12V battery. Connecting one of the battery terminals (pick either of them) to earth will do nothing special. There will still be 12V between battery terminals, and current will only flow through the lamp if it is connected to battery terminals. And one of the terminals will be connected to earth, setting the circuit potentials in reference to earth.

Same idea with a 3 meter stick. If you have a 3 meter stick, it will still be a 3 meter stick, at the ground level, at the bottom of the sea, or on top of a mountain. Setting where the reference level is has no effect on the stick.

  • \$\begingroup\$ Yes, of course there will no permanent current as long as there is no closed loop in the circuit. But I'm only interested in momentary electrostatic effects, discharge effect which might happen immediately after connecting the negative terminal to the earth. On what happens after that, I totally agree with you, later there nothing happens by same argument since my two experiments not contain a closed loop. \$\endgroup\$ Aug 28, 2021 at 19:49
  • \$\begingroup\$ But the question of my interest is what happens at the instant we connect the earth to the negative teminal? First of all the negative terminal aka a Galvanic half cell consists of a magnesium bar dipped into the electrolyte solution, a mixture of MgSO_4 and water. Since magnesium is quite reactive some of the magnesium atoms in the bar give up their two electons and dissolve in the solution as Mg++ ions. \$\endgroup\$ Aug 28, 2021 at 19:50
  • \$\begingroup\$ So the bar becomes negative charged (since contains some electons) and the electrolyte solution becomes positively charged due to dissolved Mg++ ions. If we now connect the neutrally charged earth to the magnesium bar, shouldn't some electrons be absorbed be absorbed by the earth, or are they "fixed" strong enough at the surface of the bar by positive Mg++ ions, such that they cannot "go away into the earth"? \$\endgroup\$ Aug 28, 2021 at 19:50

Initially there is a small current (that has very little to do with the battery, but more from natural potential differences any two objects have a potential difference between them), which you could think of as static being equalized.

After that, nothing happens, except for a very very small current traveling through the air and back to ground through the battery, the circuit looks like this so it would be less than pico amps traveling through the circuit:


simulate this circuit – Schematic created using CircuitLab

As far as the salt bridge, it would look something like this:


simulate this circuit

So unless you have a meter that can measure the resistance of air (most stop at 10^7 or 10^8 ohms) you won't see a current and it will register on the volt meter as open.

  • \$\begingroup\$ Could you elaborate in more detail the "Initially there is a small current" part? That's exactly I'm looking for in this question (since of course as long as there is nowhere a loop in the circuit, no permanent current can flow). Let's talk for the first about first experiment where we connect the negative terminal to earth. When we but the magnesium bar into the electrolyte solution some of magesium atoms give up their two electrons and dissolve as Mg++ ions in the solution. \$\endgroup\$ Aug 28, 2021 at 19:31
  • \$\begingroup\$ So the magnesium bar contains certain amount of nagatively charged electons in it (see picture 2) and we connect now the earth to it. he question is what precisely is your "Initially there is a small current" there. That some of these electons are absorbed by the earth? On the other hand how strong is the force of the dissolved Mg++ ions swimming in the solution. Do they completely prevent the electons in the magnesium bar to flow to earth or not? \$\endgroup\$ Aug 28, 2021 at 19:32
  • \$\begingroup\$ I should have clarified that, there's a small flow of electrons, but if you connect any two conductors in the physical world there is a small flaw of electrons because almost never are no two objects are at the same potential (they might be close). It's got nothing to do with the battery, but more to do with its probably not the same potential \$\endgroup\$
    – Voltage Spike
    Aug 28, 2021 at 23:12

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