1. The problem statement, all variables and given/known data A battery is known to have an EMF of 5.0 V but when a certain voltmeter is connected to it the reading is 4.9 V. The battery can deliver a current of 0.40 A when connected to a resistance of 12 Ω. What is the resistance of the voltmeter? Answer: 24.5 Ω. 2. The attempt at a solution Let's find the internal resistance first: E = I (r + R) → 5 = 0.40 = (r + 12) → r = 0.5 Ω. Then we have 4.9 = 5 - I r → I = 0.2 A and the resistance is R = V / I = 4.9 / 0.2 = 24.5 Ω. Is this correct? I am mostly unsure why do we look for current in here 4.9 = 5 - I r. The internal resistance is in series with the battery and the current is equal to 0.4 A.