Capacitors with unequally charged plates?

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Discussion Overview

The discussion centers around the behavior of capacitors with unequally charged plates, exploring whether it is possible to have different magnitudes of charge on each plate, such as +Q on one plate and -2Q on the other. Participants examine theoretical scenarios, practical implications, and the conditions under which such configurations might occur.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if a capacitor can function with unequal charges on its plates, suggesting a scenario with +Q and -2Q charges.
  • Another participant acknowledges that while different amounts of charge can theoretically be stored, real-world circuits typically do not operate this way, as capacitors are usually charged equally when connected to a circuit.
  • A different perspective is introduced, where a capacitor placed on a positively charged Van der Graaf ball could exhibit an excess of positive charge on both plates, leading to a small imbalance that might be more significant in RF circuitry.
  • One participant asserts that when connected to a battery, the charges on the plates of a capacitor must be equal, emphasizing that unequal charges cannot exist in that configuration.
  • Another participant counters that it is possible to independently charge the plates of a capacitor, suggesting that a net imbalance could be achieved without a battery, with specific charge values provided as an example.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of having unequal charges on capacitor plates. While some argue that equal charges are necessary when connected to a battery, others propose scenarios where independent charging could lead to imbalances. The discussion remains unresolved with multiple competing views.

Contextual Notes

Participants highlight the conditions under which capacitors operate, including the implications of connecting to a battery versus independent charging. There is an acknowledgment of practical limitations in real-world applications and the potential for significant imbalances in specific contexts like RF circuitry.

gralla55
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I'm currently on the chapter on capacitors in my physics book. I'm starting to get the concept, but everything still isn't crystal clear. I get that you can store charges in two plates, one containing a charge of Q, and the other a charge of -Q. But, would it not also work if the charges where unequal to each other in magnitude? Say, if you have one plate with +Q charge and another with -2Q ? Sorry if this is a really obvious question, haha.
 
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Sure, you can store different amounts of charges on each plate, but you probably won't find any real world circuits that do that. Capacitors are placed into circuits uncharged and neutral, and the circuits aren't usually capable of charging each plate separately.
 
If you connect a capacitor to a battery and then put it all on top of a Van der Graaf ball (say, positively charged), there will be an exess of positive charge on both plates of your capacitor. Hence the two pates will have different net charges on them, the positive plate having more and the negative plate having fewer.
Mostly, because the capacity between capacitor plates is much higher than the capacity of the individual plates to Earth and the voltages are all 'low', there will be a very small value of unbalanced charge. But you could say that your suggestion nearly always applies - just not to any significant degree.
In RF circuitry, which could involve C values of only a few pF, the imbalance could be much more significant (although the values of actual charge would be tiny).
 
one thing to get clear in your thinking is that if you connect a capacitor to a battery the charge on each plate MUST be equal. The charge removed from one plate is placed on the other plate... so equal.
If you have 2 plate with different charges it cannot be a capacitor connected to a battery.
 
The capacitor in the OP was not connected to a battery, though. But I think I am still right under those circumstances. Charge the capacitor with +1C on one terminal and -1C on the other, then charge each plate (independently) with another +0.001C (involving a lot of volts, of course). The net result will be +1.001C on one and -0.999C on the other.
I don't think the addition of a battery should alter that.
 

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