Midterm 1 Show Work Problem 2 - Homework 6 Question 7

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For the problem 2 (show work problem) in midterm 1, what are the answers for a,c, and d?

Also, can you explain part a and b for homework 6 problem 7.

(a) Find the current in the 30.0-Ω resistor.
.167  A

(b) Find the potential difference between points a and b.
5.84  V

I understand how to find the equivalent resistance. After that, i don't understand how to find the current through 30 and the potential difference.

thank you

asked Dec 10, 2014

1 Answer

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For two parallel connected capacitors, the total charge equals the sum of the charges on each of them. The charge does not escape from the capacitors, so the total will still be the same.

For part (c), with the total charge and equivalent capacitor, we can find the potential difference $2Q_0=C_e\Delta V$.

With $\Delta V$ found, the charge on each capacitor would be $Q_i=C_i\Delta V$.

For the circuit problem. First you can find the equivalent resistor ($R_e$) for the four resistors (10, 5, 5, R). The $R_e$ is in series with the other 10 Ohm resistor next to the battery. Then you can find the total current through the batter and the effective resistor. The voltage across the effective resistor is equal to $V_{ab}$. So you can find that with $V_{ab}=R_e\bullet I_{tot}$.

Once $V_{ab}$ is found, the current going through the branch including R and 5 Ohm can be found $V_{ab}=I_R\bullet(R+5.0)$.
answered Dec 10, 2014 by (21,750 points)