1. The problem statement, all variables and given/known data Power supply of EMF = E and internal resistance of R. Need E and R. This is connected to resistor of 10'000 Ohm. The current drawn from the power supply is 0.91A. A voltmeter of internal resistance 10'000 Ohm is connected in parallel to the resistor. The voltmeter reads 8.3 Volts. Original question (number 2) can be found here: https://www.dropbox.com/s/n842i3ojnanhtxc/2013-01-13 14.37.43.jpg 2. Relevant equations V = IR and Terminal PD = E - IR, presumably. 3. The attempt at a solution Overall plan: Use the two situations to set up two simultaneous equations, then solve for E and R. I'm assuming the questions is saying that the drawing of the current was independent of connecting the voltmeter. From 1st part: V = IR, R = 10'000 Ohm I = 0.91A So V = 9'100 V V = terminal PD so: 9'100 = E - 0.91×R (Call this 1) From 2nd part: Total resistance of Voltmeter and resistor is: 1/10000 + 1/10000 = 1/5000 so R_tot = 5000 Ohm. Voltage measured is terminal voltage (8.3V) Current is I = V/R = 8.3/5000 = (C 0.00166 A So: 8.3 = E - 0.00166×R (Call this 2). HOWEVER: combining 1 and 2 gives a negative internal resistance! Any ideas what I've done wrong? Thanks guys!