1. The problem statement, all variables and given/known data Find the current across 5 ohm resistor 2. Relevant equations Superposition theorem. Other voltage sources become short circuit and current sources become open circuit. Ohm's law. I = V / R 3. The attempt at a solution Using superposition theorem, we get: When only left side 10 V source is there, is short circuit across right side 10 V source, so current through 5 ohm resistor is zero. It's the same when only right side 10 V source is acting. So total current across 5 ohm resistor is zero. Book says: we cannot have voltage sources of different magnitude in parallel and that current cannot be determined. For voltage sources of same magnitude in parallel, take only one voltage source and apply ohm's law. I'm confused. Why should we ignore other voltage source? Isn't parallel operation of transformer same as above case? Like the load sees two voltage sources in parallel?