The number of complete waves passing a fixed point per second is referred to as

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

Answer: (D)

Frequency is the number of complete waves passing a fixed point each second. In ultrasonic testing this is measured in hertz (often megahertz for UT), and it tells you how fast the wave cycles occur at that point. This differs from wavelength, which is the distance between successive crests and depends on both the wave speed and its frequency (wavelength = velocity / frequency). The period is the time for one cycle (the inverse of frequency), and amplitude is how strong or tall the wave is, not how often waves pass a point. In practice, higher frequency gives better resolution but less penetration, while lower frequency penetrates deeper but with lower resolution.