Let's consider an electrical circuit consisting of a battery, some resistance and a parallel plate capacitor.

If the space between the two plates of the capacitor is replaced by a conducting fluid (perfect conductor), will there still be any charge accumulation on the plates? (As electrons can now move from one plate to another)

Can we simply replace the capacitor with a conducting wire in this scenario and thus conclude that the current in the circuit is constant and doesn't vary with time?

  • $\begingroup$ Assume it's a perfect conductor, no need to consider electrochemistry. $\endgroup$ Sep 11, 2023 at 14:44
  • 2
    $\begingroup$ To some degree, this a real device: the mercury switch! When a mercury switch is closed, it does just act as a wire. When it is open, you've got two metal terminals near each other, so you have a capacitance (though a small, unwanted one). $\endgroup$
    – HTNW
    Sep 11, 2023 at 14:51

1 Answer 1


Putting conducting fluid into a capacitor is equivalent to connecting a resistor in parallel with the capacitor. The more conductivity, the less resistance. This means that the capacitor will discharge over the time.

Note, that filling the capacitor with some new substance will likely change the permittivity of the space between the plates, and thus change the capacitance as well.

If it's, as you say, a perfect conductor, this is equivalent to shorting the capacitor, which makes it no longer play any role in the circuit.

  • $\begingroup$ Thank you that was my doubt $\endgroup$ Sep 11, 2023 at 14:48

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