What term describes the number of times a wave moves up and down in a given time?

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

Answer: (D)

Frequency is the rate at which something happens per unit time. For a wave, it tells you how many complete up-and-down oscillations occur in one second. So counting how many times the wave moves upward and downward in a given time directly measures its frequency. Wavelength is the spatial distance between successive peaks, amplitude is how far the wave moves from rest, and period is the time for one complete cycle (which is the reciprocal of frequency). In SI units, frequency is measured in hertz, or cycles per second. For example, five complete up-and-down cycles in one second means a frequency of five hertz.