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I have edited my explanation. I hope this helps.

When a capacitor is charging where is the source of or where are the electrons coming from that deposit themselves on the capacitor surface on the positive end. Do they come from the battery or are inside the wire?

Sedumjoy
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    At all times, for all circuits, the charge flowing in and out of a component are exactly equal, so that the net charge entering a component is zero. This means that in your circuit, the battery current, and the wire current and the capacitor current are exactly equal. If one electron enters a terminal on the capacitor, another electron exits at the same time. The same is true for the wire and the battery also. Capacitors do not store charge, in that sense. – user57037 Mar 04 '17 at 18:50
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    _"... as the capacitor is charging the current is not flowing through the capacitor ..."_ - Your premise is false; the current _is_ flowing through the capacitor. – marcelm Mar 04 '17 at 19:01
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    I'd argue that point @marcelm, but I don't want to muddy the question. – Trevor_G Mar 04 '17 at 19:11
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    It's called a displacement current and isn't actually a flow of electrons through or across or around the capacitors dielectric. It amounts to the same as real current though! – Andy aka Mar 04 '17 at 19:49
  • I know current does not flow through the capacitor. I believe that is a well established – Sedumjoy Mar 04 '17 at 21:02

2 Answers2

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In a discharged capacitor, each of the two plates of the capacitor is electrically neutral. Neutral means that there are for each atom of the plates there is an equal number of positive protons in the nucleus and negative electrons in the hull of the atom. Thus the number of all the positive and negative charge carriers inside the plates is in ballance.

Now if the capacitor is changed, for every electron that is removed from the positive plate, another electron is added to the negative plate. The battery is only "pumping" the electrons from the positive plate to the negative plate.

If a charged capacitor is discharged over a resistor, electrons are flowing from the negative plate through the resistor to the positive plate. Discharging is finished if both plates are electrically neutral again and no more current is flowing through the resistor.

Uwe
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  • It sounds like you are saying the electrons are coming from the capacitor itself ? or do you mean the electrons are coming from the battery. I assume they are not coming from the battery since there is no current flowing through the capacitor. – Sedumjoy Mar 05 '17 at 01:14
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    @Sedumjoy the electrons during the charging DO come from the battery. The fact that there is no current across the capacitor does not imply that there is no current at all from the battery. It is explained well in the answer, please reread the 2nd paragraph. – Claudio Avi Chami Mar 05 '17 at 05:22
  • Yes , I finally got it now. Comes from both! Since in a sense there already are electrons in the wire ( drift) but the battery has to also supply electrons as you say in order for the capacitor to build charge. Thank you. – Sedumjoy Mar 05 '17 at 18:30
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Consider the bathtub-bucket image below.

enter image description here

The bathtub on the left is connected to a bucket through a valve.

When you open the value the water will flow from the bathtub to the bucket. The rate at which the water flows, starts out fast and exponentially decays as the bucket reaches the same height as the bathtub water.

This is the same as a battery and a capacitor. The Battery is the bathtub and the capacitor is the bucket. Electrons are the water. When you close the switch, electrons move from the battery and "fill up" the capacitor till it reaches the same voltage as the battery.

The water does not go "through" the bucket, but it DOES go through the pipe. In the circuit, the is no current through the capacitor, but there IS current in the wires between the battery and the capacitor until the capacitor is fully charged.

Trevor_G
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