Does the charge of a capacitor change during immersion?

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Discussion Overview

The discussion revolves around whether the charge of a capacitor changes when it is immersed in a liquid, specifically distilled water. Participants explore the theoretical and practical implications of capacitance and charge conservation in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that theoretically, the charge of a capacitor cannot change unless there is a current, implying that immersion should not affect charge if no current flows.
  • Another participant notes that in practical scenarios, leakage currents could lead to changes in charge, challenging the theoretical perspective.
  • A participant reiterates the initial question about the relationship between capacitance and charge, questioning how immersion affects these variables and whether energy stored in the capacitor changes as a result.
  • It is mentioned that while charge is conserved, capacitance and voltage may change upon immersion, indicating a distinction between charge and other electrical properties.

Areas of Agreement / Disagreement

Participants express differing views on the impact of immersion on charge, with some asserting charge conservation and others highlighting practical factors like leakage currents that could alter charge. The discussion remains unresolved regarding the specific effects of immersion on charge and capacitance.

Contextual Notes

Participants acknowledge the theoretical framework of capacitance (C = εA/d) and its dependence on the dielectric constant (ε), but the implications of changing ε during immersion are not fully resolved. There is also uncertainty regarding the energy dynamics in the system upon immersion.

Who May Find This Useful

This discussion may be of interest to those studying capacitor behavior in different media, electrical engineering students, and individuals exploring theoretical versus practical aspects of capacitance and charge conservation.

halo168
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If given a capacitor with stored charge, would its charge remain constant before and after it is immersed in a liquid (i.e. distilled water)? Why?

I know that before immersion, the capacitance would be = (ɛAV/d), but would that be the same if immerged in distilled water?
 
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If you are asking theoretically without regard to practical realities, then the charge can't change unless there is a current in or out. The capacitance can change, but not the charge if there is no place for the charge to go.

In real life, there are nonzero leakage currents that negate that answer.
 
halo168 said:
If given a capacitor with stored charge, would its charge remain constant before and after it is immersed in a liquid (i.e. distilled water)? Why?

I know that before immersion, the capacitance would be = (ɛAV/d), but would that be the same if immerged in distilled water?
It looks like you are combining two equations...

Q=CV
C=εA/d

When you immerse the capacitor that has nothing between the plates in distilled water, assuming no leakage current, the charge on the plates will not change. So what happens in the first equation? ε changes (by how much?) in the 2nd equation, so what does that do to the first equation?

And since the energy stored in the capacitor is E=CV^2/2, is there a change in the energy stored in the system? If so, where did the extra energy come from or go to? :smile:
 
I think what you are referring to is the capacitance changing. A very important rule regarding capacitors is that charge is always conserved (unless actively changed by a current or voltage). While the charge is always conserved, capacitance can change and voltage as well. The capacitance and voltage might go up or down when immersed, but never the charge.
 

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