1. The problem statement, all variables and given/known data A circuit is constructed with five resistors and one real battery as shown above right. We model. The real battery as an ideal emf V = 12 V in series with an internal resistance r as shown above left. The values for the resistors are: R1 = R3 = 59 Ω, R4 = R5 = 79 Ω and R2 = 140 Ω. The measured voltage across the terminals of the batery is Vbattery = 11.61 V. What is r, the internal resistance of the battery? 2. Relevant equations Vb = Vo((R/r)/(1+R/r)) Vb= voltage across battery terminals Vo= Internal voltage r= internal resistance R= external resistance Total ext. resistance in parallel: 1/Rt= 1/r1 + 1/r2 total ext. resistance in series: Rt = r1 + r2 3. The attempt at a solution Taking total resistance dividing by the amperage.