In ultrasonics, what is the velocity used to express the rate at which sound waves pass through a material?

• A. velocity
• B. frequency
• C. wavelength
• D. amplitude

Answer: (A)

Velocity is the rate at which sound waves propagate through a material, measured in meters per second. In ultrasonics, this speed lets you convert the time it takes for a pulse to travel (and return) into distance, since distance is speed multiplied by time (with the round-trip factor accounted for). The speed in a material depends on its properties—stiffer (more elastic) and less dense materials transmit waves faster. Frequency, wavelength, and amplitude describe other aspects of the wave: frequency is cycles per second, wavelength is the distance per cycle (related to velocity by v = fλ), and amplitude is the wave’s strength.