Circuit Analysis: Solving w/ Kirchoff's Laws for Potential Difference b/w a & b

[Sheneron]

Homework Statement

http://img185.imageshack.us/my.php?image=p2827altvk4.gif

(b) Calculate the potential difference between points a and b.

The Attempt at a Solution

I have solved the circuit using Kirchhoff's laws; I had to solve for the current in the 2 ohm resistor. But I am stuck at this question. I surmised that the potential difference would be using the 2 ohm resistor since we solved for it specifically. I found the potential difference at that resistor, and that yielded the correct answer but I have no clue why. I was wondering if someone could explain this to me? Thanks.

 

[berkeman]

Homework Statement

http://img185.imageshack.us/my.php?image=p2827altvk4.gif

(b) Calculate the potential difference between points a and b.

The Attempt at a Solution

I have solved the circuit using Kirchhoff's laws; I had to solve for the current in the 2 ohm resistor. But I am stuck at this question. I surmised that the potential difference would be using the 2 ohm resistor since we solved for it specifically. I found the potential difference at that resistor, and that yielded the correct answer but I have no clue why. I was wondering if someone could explain this to me? Thanks.

Not sure I understand your confusion. You solved for the voltages and currents in the circuit using KCL (most likely). That gives you the voltage across the 2 Ohm resistor and thus the current through it. Why don't you post your equations and solution, and point to what is confusing you about your final answer?

 

[Sheneron]

Well my question is why do I use the 2 ohm resistor to find the potential difference at points a and b?