# Why a capacitor discharges

1. Oct 22, 2011

### nik2011

Hello,

This isn't an actual homework but just a thing I'm wondering about.

Suppose we have a capacitor with plates A and B. The plates are not connected. Plate A has 10 electrons more than plate B.
Now someone connects the plates with a wire. The electrons on plate A repel each other stronger than the electrons on plate B as there are fewer electrons on plate B. And as a result there is a current from plate A to plate B.
One thing doesn't make sense to me. The electrons on plate A repel the electrons from plate B.
So on one hand there are electrons which flow from plate A to plate B and on the other hand plate A's electrons repel electrons from plate B in the direction which is opposite to this flow, then why doesn't it stop the flow?

Thank you!

2. Oct 22, 2011

### ehild

I do not understand what you mean:

Because of the excess electrons, plate A is at a negative potential with respect to B. The excess electrons on A repel each other so they move to plate B, making B negative. When the potential is equal on both plates there is no more driving force for the electrons to move. This happens when half of the excess electrons moved from A to B.

ehild