Which of the following describes alternating current?

• A. Current that flows in one direction only
• B. Current that alternates between positive and negative directions
• C. Current that is constant over time
• D. Current that only flows with a battery

Answer: (B)

Alternating current (AC) is characterized by a flow of electric charge that periodically reverses direction. This definition aligns with the correct choice since AC voltage and current waveforms typically follow a sine wave pattern, fluctuating between positive and negative values over time.

This back-and-forth movement of charge carriers distinguishes alternating current from direct current (DC), where the flow of electricity is constant and in one direction. AC is commonly used for power distribution because it is more efficient for transmitting electricity over long distances, allowing for the use of transformers to step voltage levels up or down.

In contrast, other options describe characteristics that do not represent alternating current. For instance, current that flows in one direction only refers to direct current, while constant current refers to a scenario where the electrical current does not change over time, again applicable to direct current. Additionally, stating that current only flows with a battery implies a direct current scenario because batteries typically provide DC power.

Overall, understanding that alternating current alternates its direction is fundamental to grasping the principles of AC electricity and its applications in various devices and power systems.