1. The problem statement, all variables and given/known data A battery has an emf E and an internal resistance r. IT is connected to an external resistor R. When R=4 ohms, the potential difference is 9.5 V. When R = 6 ohms, the potential difference is 10.0 V 2. Relevant equations 3. The attempt at a solution Rtotal = R + r I = V/Rtotal E = V/Rr + V_ba when I equate both to try to solve for r, I still end up getting an unknown of 2 variables. Any help would greatly be appreciated. Thank you.