What is the frequency range for ultrasound?

Ultrasound refers to sound waves that have frequencies above the audible range for humans, which is generally considered to be up to 20,000 Hz, or 20 kHz. The correct choice highlights that ultrasound operates at frequencies above this threshold. This characteristic makes ultrasound useful in medical imaging and therapeutic applications, as it can penetrate tissues and provide information about the internal structures of the body without the harmful effects associated with ionizing radiation.

The frequencies below 20,000 Hz fall into the category of audible sound, while frequencies below 10,000 Hz are typically considered sub-audible. Thus, choices indicating ranges below 20 kHz do not align with the definition of ultrasound. Hence, 20,000 Hz and above is indeed recognized as the frequency range for ultrasound applications in various fields, including medicine and industrial testing.