Which frequency qualifies as ultrasound?

Ultrasound is defined as sound waves with frequencies that are above the range of human hearing. The threshold of human hearing is generally recognized as 20 kilohertz (20,000 hertz), which corresponds to 20 kilocycles per second. Therefore, any frequency above this threshold is classified as ultrasound.

Frequencies that are classified as ultrasound are typically used in various applications such as medical imaging, diagnostic procedures, and therapeutic treatments. Understanding that ultrasound starts at frequencies greater than 20 kilohertz is essential for distinguishing it from audible sound, which only encompasses lower frequencies.

The key point is that the correct choice identifies that ultrasound begins at frequencies exceeding 20 kilocycles per second, reinforcing the understanding of the frequency threshold that differentiates audible sound from ultrasound.