# RC Circuit Test Question

## Homework Statement

Okay, I don't EXACTLY remember the problem statement or the circuit diagram, but I believe I can give enough information to do the problem. On this past quiz, I got 75/100, where there are 4 parts: 2 short answer, 1 part multiple choice, 1 part group test. I got 25 on MC, the group, and 24 on one of the short answer. This RC circuit question I got 1/25! I haven't gotten it back yet, but I thought I knew what I was doing.
There was a one-loop (obviously series) RC circuit, with, in order from first to last going counter-clockwise from the right side of the loop, an ideal battery, a switch, a capacitor, a resistor, another capacitor, then another resistor. Basically it went
(A)__R2___C2_(B)_R1__C1__ \__
l************************l
l************************+
l************************V
l************************-
l___________________________l
(Please ignored the asterisks, it was only a method applied to keep the spacing of the rectangle of the loop there in the post.)
Then it asked to calculate the potential and current at time=0 at (A) and (B), then at t=infinity.

## Homework Equations

Kirchoff's Loop Rule: sum of voltages is 0
differential equation with charge term and time derivative of charge

## The Attempt at a Solution

Current at t=0 is 0A for both (A) and (B) because, I forgot to put it down in the statement, but it said the capacitors are initially uncharged. I also said that the potential at both are equal to the battery's voltage, but now that I think about it, that doesn't sound plausible since there is no current. At t=infinity, I used Kirchoff's Loop Rule to solve for the current I
0=V-Q/C1-IR1-Q/C2-IR2 ---> I(t)=e^(-t/((R1+R2)C(eq)))
since the current should be everywhere the same on a series circuit. Then, for the potentials, I used Kirchoff's Loop Rule, but for (B) I took out the last two terms since the current "hasn't hit them" to drop the potential. I added the last two terms and solved for (B). Is this incorrect? I seem to be doubting myself now that I only got 1/25, which is like no partial credit. I filled the entire page with work. I also remember when calculating C(eq), I forgot to take 1/C(eq) after using 1/C(eq)=1/C1+1/C2. But that was used throughout the problem, so wouldn't that be double jeopardy to keep charging for that? I'm not sure, I need help please.

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