Which term describes current that changes direction periodically?

Which term describes current that changes direction periodically?

• A. Direct Current (DC)
• B. Generator
• C. Transformer
• D. Alternating Current (AC)

Answer: (D)

The current that changes direction periodically is alternating current. In alternating current, the flow of charge reverses sign in a regular cycle, described by a waveform that goes positive and then negative over time. This is different from direct current, where the charge flows in one constant direction. A handy picture is a sine wave: it rises from zero to a positive peak, crosses zero, goes to a negative peak, and returns. This back-and-forth flow happens naturally in a generator, because as the coil spins in a magnetic field, the induced voltage flips sign every half turn, creating a repeating cycle. That’s why power grids use alternating current—they’re tied to how generators operate and how voltage can be transformed efficiently. Transformers rely on changing currents to work, which is another reason AC is the standard for distributing electricity. The term describes the type of current itself, not a device, so it correctly identifies the back-and-forth flow of current over time.

The current that changes direction periodically is alternating current. In alternating current, the flow of charge reverses sign in a regular cycle, described by a waveform that goes positive and then negative over time. This is different from direct current, where the charge flows in one constant direction.

A handy picture is a sine wave: it rises from zero to a positive peak, crosses zero, goes to a negative peak, and returns. This back-and-forth flow happens naturally in a generator, because as the coil spins in a magnetic field, the induced voltage flips sign every half turn, creating a repeating cycle. That’s why power grids use alternating current—they’re tied to how generators operate and how voltage can be transformed efficiently.

Transformers rely on changing currents to work, which is another reason AC is the standard for distributing electricity. The term describes the type of current itself, not a device, so it correctly identifies the back-and-forth flow of current over time.