Which term describes a current that varies in voltage and polarity over time?

Which term describes a current that varies in voltage and polarity over time?

• A. Direct current
• B. Pulsating current
• C. Static current
• D. Alternating current

Answer: (D)

A current that changes both voltage and direction over time is alternating current. In AC, the voltage rises and falls and regularly reverses polarity, so the direction of current flow flips with each cycle. The common waveform is sinusoidal, matching what’s delivered by household electrical outlets and power grids. In contrast, direct current stays in one direction with roughly constant polarity; pulsating current varies in magnitude but does not reverse direction, and static current implies no change at all. So the term that best fits a current varying in voltage and polarity over time is alternating current.

A current that changes both voltage and direction over time is alternating current. In AC, the voltage rises and falls and regularly reverses polarity, so the direction of current flow flips with each cycle. The common waveform is sinusoidal, matching what’s delivered by household electrical outlets and power grids. In contrast, direct current stays in one direction with roughly constant polarity; pulsating current varies in magnitude but does not reverse direction, and static current implies no change at all. So the term that best fits a current varying in voltage and polarity over time is alternating current.