The rate at which the current changes direction in AC is called what?

• A. Amplitude
• B. Frequency
• C. Wavelength
• D. Phase

Answer: (B)

In AC, the current reverses direction in a repeating pattern, and the number of complete cycles that occur each second tells you how quickly that reversal happens. That rate is frequency, measured in hertz. It directly describes how fast the oscillation repeats, i.e., how often the current changes direction per second. For example, typical mains power runs at 60 Hz, meaning the waveform completes 60 cycles each second. The period of one cycle is the inverse of frequency (T = 1/f). Amplitude refers to how large the current is, wavelength is a spatial property of waves, and phase is the relative offset between waves, not the rate of reversals. So frequency is the best description of how fast the current changes direction.