# Homework Help: RC circuit complete

1. Aug 12, 2014

### ajcoelho

1. The problem statement, all variables and given/known data

My question is very simple and perhaps it has an obvious answer.

So, if we have a simple RC circuit with and EMF battery, a resistance and a capacitor, when the capacitor is charging, electrons leave the negative terminal of the battery and accumulate on one of the capacitor plates. This way, how is there a current on the other side of the circuit? If electrons accumulate in one side of the capacitor, they will not "complete" the circuit, right?

On the other hand, when the capacitor is full charged, how does the EMF "knows it" and stop "sending" electrons out? :tongue:

2. Aug 12, 2014

### Zondrina

Initially, when the plates are uncharged, the potential difference between them is zero. As the plates become oppositely charged, the potential difference between the plates increases until it equals the potential difference between the terminals of the battery.

At that point, the positive plate and the positive terminal of the battery are at the same potential and there is no electric field in the wire between them.

Similarly, the negative plate and the negative terminal reach the same potential and there is no electric field in the wire between them.

With no electric field in the wire, there is nothing to do work on the charge carriers to drive them. Hence the flow stops and the capacitor is then fully charged with $q = CV$.

3. Aug 12, 2014

### ehild

The negative charge accumulated on one plate of the capacitor repulses the free electrons of the other plate so they flow towards the positive terminal of the battery.

ehild