1. The problem statement, all variables and given/known data Basically, my task is to find out the internal resistance of a solar cell. I set-up a circuit as seen here (http : / / mt14 . quickshareit . com / share / picture666d18 . png), and measured the Current and Voltage on different settings of resistance in 5Ohm intervals from 0 Ohms to 50 Ohms. Now that I have calculated the resistance from the measured voltage and current, the resistance remains higher that the controlled resistance (on the variable resistor), however at 35 Ohms of controlled resistance, the calculated resistance drops below the controlled resistance. The data can be found here (http : / / mt15 . quickshareit . com / share / picture58258f . png). Is this normal behaviour? Also, what am I to make of these results? 2. Relevant equations R = V/I E = Ir + V E = V + v V = (-r) I + E 3. The attempt at a solution Above, in the attached images. Please note that due to the 15 post requirement before posting links, I have had to place spaces before and after each dot and slash.