# Homework Help: Capacitor in a Parallel Circuit

1. Apr 23, 2013

### PhotonTrail

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

I'm not sure how to put this in words, but I shall try. Alternatively, I've attached an image. It's hand-drawn, but I hope it's legible enough.

Imagine a circuit drawn in the shape of a rectangle, with a single resistor $R_1$ on the top side, plus a DC cell $\epsilon_2$ and a second resistor $R_3$ on the bottom side. Now connect the left and right sides of the rectangle with a horizontal line in the middle. This portion of the circuit contains the following: a capacitor $C_1$, a second DC cell $\epsilon_1$, and a third resistor $R_2$.

Question: What are the currents at every point in the circuit?

2. Relevant equations

None.

3. The attempt at a solution

I would say that the portion of the circuit with the capacitor has no current flowing through, i.e. $I_2=0$. I originally thought too that $I_1$ and $I_3$ are equal to zero too, because I found it difficult to accept that there will be current flowing in the other parts of the circuit if there is no potential difference across the middle branch.

Am I mistaken in thinking that $I_2$ is zero? If I am not, am I wrong in assuming that the potential difference between the left and right sides of the middle branch is zero? If I am still not, then why do the top and bottom branches have currents flowing? How do the potential differences work out?

Many thanks for any assistance!

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2. Apr 23, 2013

### SammyS

Staff Emeritus
You are not mistaken about this. The current, $\ I_2\,,\$ is zero.

... Well, it's zero if the capacitor is not charging or discharging.

Yes. You are wrong about this. That $\ I_2=0\$ only means that the voltage drop across R3 is zero. The is a potential difference across $\ \varepsilon_1\$ and also across the capacitor.

3. Apr 23, 2013

### PhotonTrail

Forgot to mention that it's in steady state, sorry!

Ahh I see it now. What an embarrassing blunder. Thanks a bunch! :)