# Potential -- Find the potential at node 3

1. Aug 12, 2014

### Rectifier

The problem
What is the potential at node 3, if the potential at node 1 is 0?

The attempt
If I start at node 1 and move towards node 3
1->2
-5V
2->3
+(-3V)
1->3
-5+(-3)=-8V

If I start at node 3 and move towards node 1
3->2
-(-3)
2->1
5
3->1
3+5=8V

I am not really sure what is right here.

2. Aug 12, 2014

### Staff: Mentor

The problem looks overconstrained and inconsistent. Where is it from?

And when you go in the direction of - to +, that is an increase in potential. I get 2 different answers for going the 2 different ways from node 1 to node 3...

3. Aug 12, 2014

### bennyq

KVL in the loop, starting at 3..
3->2
-3v(rise)
2->1
-5v(fall)
1->4
-9v(fall)
4->3
17V(rise)
-3-5-9+17=0, so the voltage in the loop adds up.

Now from V3->V2->V1
V3-3-5=0
V3=8V
Now from V3->V4->V1
V3-17+9=0
V3=8V

Seems okay to me?

4. Aug 12, 2014

### Staff: Mentor

Ah, I see what fooled me. They labeled the right-hand voltage as negative, instead of relying on the +/- signs to determine the direction of the voltage. That's very non-standard in electronics, but I guess I should have seen that trick part of the question. Thanks for clearing that up!