Which quantity's direction helps determine voltage polarity?

• A. Current
• B. Direction
• C. Resistance
• D. Current flow

Answer: (D)

Voltage polarity is set by the direction in which current flows through a component. Under the common passive sign convention, the terminal that current enters is considered positive. So knowing how current moves tells you which side of the element is at higher potential, and thus the polarity. For a resistor, the voltage drop aligns with the current’s path: the entry side is positive, the exit side negative. If the current were to flow the opposite way, the labeled polarity would flip. The other quantities don’t by themselves fix polarity: the magnitude of current doesn’t indicate sign, direction alone needs a reference, and resistance is about how much voltage is needed for a given current, not which end is positive.