In opposing two sources, current is determined by

• A. The net voltage and the total resistance
• B. The highest voltage source alone
• C. The number of sources
• D. The smallest voltage source alone

Answer: (C)

When two sources oppose, the current is driven by the net voltage across the circuit and the total resistance it must push through. The net voltage is found by taking the algebraic difference of the source voltages, respecting their polarities. The current then follows Ohm’s law: I = V_net / R_total. The total resistance is everything the current encounters in the path (for a simple series setup, the resistances add up; in more complex networks you use the appropriate equivalent resistance). If the opposing sources have equal voltages, the net voltage is zero and the current is zero regardless of resistance. So, the number of sources matters only insofar as it changes the net voltage; the actual current comes from that net voltage relative to the total resistance.