What is Alternating Current (AC)?

• A. Direct Current, a current that travels in one direction
• B. Pulsating current
• C. Random current
• D. Alternating Current, a current that changes directions

Answer: (D)

Alternating current is defined by its direction reversing over time. The current flows back and forth, typically in a smooth, repeating waveform, so electrons oscillate rather than drift steadily in one direction. This reversal happens at a specific frequency (for household power, usually 50 or 60 Hz), and the voltage and current rise and fall as the waveform progresses.

This is why it’s used for power distribution: the reversal makes it easy to transform voltages up or down with transformers, enabling efficient long-distance transmission. In contrast, direct current flows in one direction with a relatively constant magnitude, which is not the characteristic of AC. A pulsating current changes in magnitude but does not change its direction, and a random current has no regular, predictable reversal pattern. So the defining idea is that the current changes directions.