True statement about ultrasound frequency?

• A. It is greater than 20,000 cycles per second
• B. It is less than 20 cycles per second
• C. It equals the frequency of visible light
• D. It only applies to diagnostic imaging

Answer: (A)

Ultrasound is defined by its frequency being above the range of human hearing, which ends around 20,000 cycles per second. So a frequency greater than 20,000 Hz correctly characterizes ultrasound. Frequencies below that fall into the infrasonic range, not ultrasound. Visible light operates at frequencies many orders of magnitude higher than ultrasound, so equating them is incorrect. And ultrasound isn’t limited to diagnostic imaging; while imaging is a common use, the frequency concept applies across therapeutic applications too, though imaging typically uses higher (megahertz) ranges.