Which statement correctly describes alternating current (AC)?

Which statement correctly describes alternating current (AC)?

• A. Current flows in one direction.
• B. Voltage is constant.
• C. Current changes direction periodically.
• D. Current is zero throughout.

Answer: (C)

Alternating current is defined by current that reverses direction periodically. In AC, the instantaneous current rises and falls as the voltage cycles, so it flows first in one direction and then in the opposite, typically following a sinusoidal pattern. This means the polarity of the voltage and the direction of current change over time, repeating every cycle (at the standard frequency like 50 or 60 Hz). That’s why the statement is correct: it captures the fundamental behavior of AC. The other descriptions don’t fit AC—the current doesn’t flow in only one direction, the voltage isn’t constant (it varies with time and reverses polarity), and the current isn’t zero throughout—there is ongoing, time-varying current in an AC system.

Alternating current is defined by current that reverses direction periodically. In AC, the instantaneous current rises and falls as the voltage cycles, so it flows first in one direction and then in the opposite, typically following a sinusoidal pattern. This means the polarity of the voltage and the direction of current change over time, repeating every cycle (at the standard frequency like 50 or 60 Hz). That’s why the statement is correct: it captures the fundamental behavior of AC. The other descriptions don’t fit AC—the current doesn’t flow in only one direction, the voltage isn’t constant (it varies with time and reverses polarity), and the current isn’t zero throughout—there is ongoing, time-varying current in an AC system.