The potential difference across the terminals of a battery is 8.20 V when there is a current of 1.54 A in the battery from the negative to the positive terminal. When the current is 3.56 A in the reverse direction, the potential difference becomes 9.40 V. What is the internal resistance r of the battery?
V_ab = E - Ir
The Attempt at a Solution
So I thought that it would make no difference if the charge was reversed. So I just plugged the values into the equations, so since I have two equations and two variables I could solve for r.
8.56 = E - 1.54r -> E = 8.56 + 1.54r
9.40 = E - 3.56r -> E = 9.40 + 3.56r -
0 = -.84 - 2.02r
r = -.416
Obviously the resistance can't be negative. What am I doing wrong, does it have something to do with the reversing part of the problem?