1. The problem statement, all variables and given/known data Find potential difference Vab between points a and b on the figure. All resistances and emf’s are indicated, note the polarity of the batteries. What happens if the polarity of E1 is reversed (polarity of E2 kept the same) and both emfs are made equal? 2. Relevant equations Okay, so you definitely need to use Kirchoff's rules here. I also read in my text that if you want to find Vab all you do is go from point b to point a on your circuit (I'm wondering if me solution is too simple) (I did make a circuit through a program however that proves my answer. 3. The attempt at a solution For the first part I got that Vab= -(R2(I1+I2)) (I1 and I2 come from E1 and E2) also, I saw that with switching E2 there is no current through R2. I am not sure why this is true though, is it because a path goes through the least resistance?