# Simple circuit analysis w/ voltage sources - MasteringPhysics wrong?

1. Mar 1, 2013

### resigned

1. The problem statement, all variables and given/known data
We are given a simple circuit with 4 resistors, a known voltage source, and an unknown voltage source. The photo is below in my solution attempt.

2. Relevant equations
V=IR, R(parallel)=(1/R1+1/R2)^-1

3. The attempt at a solution
I found the voltage drop over the given resistor, then used that voltage to find the current through the other resistor in parallel, which gave me the total current through the circuit.

http://imgur.com/HtJootR

My problem is I am pretty sure MasteringPhysics is wrong here. I included all of my work finding my answer, and then tested their answer to show that it is wrong. I am confident in my work but was hoping you could look it over before I go make a dodo of myself to my instructor.

2. Mar 1, 2013

### Staff: Mentor

Re: Simple circuit analysis w/ voltage sources - MasteringPhysics wron

Their answers look fine to me.

Write out the voltage drops across each resistor. You know that they will potential drops in the direction of current flow, and that current flow can be either clockwise or counterclockwise. Perform a "KVL walk" around the loop assuming that the current flows in one direction and solve for the required Vba. Then do the same again assuming the current is flowing in the other direction.

By the way, that's a 1.0Ω resistor on the bottom, not a 1kΩ resistor.

3. Mar 1, 2013

### resigned

Re: Simple circuit analysis w/ voltage sources - MasteringPhysics wron

Consarn it. I think that's the source of my problems. I didn't notice it had different units to the rest of them.