# Need help with basic circuit

Discussion in 'Homework Help' started by ziggy1212, Oct 11, 2009.

1. ### ziggy1212 Thread Starter New Member

Oct 10, 2009
3
0
I need help finding the voltage across A & B. I know that I = 1A (left loop) and I = .5A (right loop). I also know the voltages at each node, but what is my equation to find the voltage across A and B. Each time I have worked it, I get a different answer.

1st try=> {Left loop} 2V (top left node) 6V (top right node) {Right loop} -4V (top left node) 6V (top right node)
2nd try=> {Left loop} -10V (top left node) -6V (top right node) {Right loop} -16V (top left node) -6V (top right node)

Still, I am confused. Do I trace the entire circuit to get voltage across A & B or just the middle U.

Last edited: Oct 11, 2009
2. ### halp New Member

Oct 11, 2009
8
0
Do it however you want. The middle U is the shortest way, but you can go around if you want, the result will be the same.

EDIT: Assuming you go the U-way;

First you have the R2 resistor; V2 = R2 * I2 = 6 * -1 = -6 (going against the current)
Then there's the battery, 12V.
And finally the third resistor, going current-wise, so 8 * 0.5 = 4V
So 12+4-6=10V total. But say you've gone around the first loop. First there's 4V (current-wise), and then -10V, which still adds up to -6V.

Last edited: Oct 11, 2009