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On RC circuit, capacitor discharges when the voltage supply is removed.

But I've learned that the net electric field outside a charged capacitor is zero by gaussian surface and gauss law.

I don't understand the mechanism. Shouldn't be there an electric field in order to make charge flow when discharging happens?

Is there an another mechanism?

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  • $\begingroup$ "But I've learned that the net electric field outside a charged capacitor is zero by gaussian surface and gauss law." - the fact that there is no net charge enclosed within the volume enclosed by the surface doesn't imply that there's zero electric field outside of that volume does it? Consider the electric field of a simple electric dipole. $\endgroup$ May 22 '20 at 14:45
  • $\begingroup$ @alfred Thanks for the reply. I've figured it out with your help. I was confused with infinite sheet of charge case $\endgroup$
    – user265256
    May 22 '20 at 15:15
  • $\begingroup$ @AlfredCentauri What you say makes sense since there is a difference between the NET flux across the surface being zero and there being no flux across the surface. But many answers on this site state there is no electric field outside a charged capacitor and they don't seem to make the distinction between flux and net flux.Your thoughts? $\endgroup$
    – Bob D
    May 22 '20 at 15:37
  • $\begingroup$ @BobD, I don't know why that would be unless they explicitly state something like "ignoring the fringing fields". If I recall correctly, I've engaged someone here (or maybe Wikipedia) before regarding the fringing fields and the fact that they are crucial for understanding and explaining some capacitor problems, i.e., you can't ignore fringing fields except for when, e.g., approximating the capacitance of a capacitor. $\endgroup$ May 22 '20 at 15:58
  • $\begingroup$ user265256, I found this slide that you may find helpful: How is Discharging Possible? $\endgroup$ May 22 '20 at 16:05
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But I've learned that the net electric field outside a charged capacitor is zero by gaussian surface and gauss law.

First, Gauss's law states that the electric flux through a closed surface enclosing a volume with zero net electric charge is zero. That does not imply that the electric field outside the volume is zero, it implies that every electric field line that originates (terminates) in the volume also terminates (originates) in the volume (even if part of the field line is outside the volume).

Here's a 'picture' of the electric field of a charged capacitor that I found at the answer here:

enter image description here

The fringing field is often ignored in elementary capacitor calculations but it must not be ignored if one is to fully explain capacitor operation.

Also, there is essentially a duplicate of your question here: Why does a capacitor discharge?

I've answered your post here just to clear up the misconception you have regarding Gauss's law.

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    $\begingroup$ Again, Thank you for your kind answer. I have understood the concepts I asked correctly with your help. I'm sad that I can't express how I am grateful of you because I'm not that good at writing english... $\endgroup$
    – user265256
    May 22 '20 at 16:38
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it is only discharged. if the two plates are connected by some resistor. otherwise it stays charged.

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  • $\begingroup$ trula, I've downvoted your answer because it is more of a comment and not an answer (it doesn't actually address what I believe to be the OP's question). $\endgroup$ May 22 '20 at 14:49

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