Which of the following is an example of a periodic current?

• A. Tidal current
• B. Steady river current
• C. Wind-driven current with constant speed
• D. Ocean current with no variation

Answer: (A)

Periodic current means the flow repeats in a regular cycle over time. A tidal current fits this idea because tides rise and fall in a predictable pattern driven by the Moon and Sun, causing the current to strengthen, weaken, and even reverse direction on a roughly 12- to 24-hour cycle depending on the location. The steady river current isn’t periodic in the same sense; it tends to stay relatively constant, with only gradual or weather-related fluctuations. A wind-driven current with constant speed would produce a steady flow rather than a repeating cycle. An ocean current with no variation obviously isn’t periodic either. So the tidal current is the example that shows periodic behavior.