Which statement is true about ultrasonic frequencies?

Which statement is true about ultrasonic frequencies?

• A. They have frequencies greater than 20 kHz
• B. They are audible to humans
• C. They are below 20 Hz
• D. They have frequencies between 1 and 2 Hz

Answer: (A)

Ultrasonic frequencies are sound waves with frequencies above the upper limit of human hearing. Humans typically hear roughly 20 Hz to 20 kHz, so anything higher than about 20 kHz is ultrasonic. That’s why the statement is true: ultrasonic frequencies have frequencies greater than 20 kHz. The other options describe frequencies outside the ultrasonic range—below 20 Hz would be infrasonic, and 1 to 2 Hz is far below human hearing as well—so they aren’t ultrasonic. In practice, ultrasound is used in applications like medical imaging and industrial testing precisely because its higher frequencies provide better resolution.

Ultrasonic frequencies are sound waves with frequencies above the upper limit of human hearing. Humans typically hear roughly 20 Hz to 20 kHz, so anything higher than about 20 kHz is ultrasonic. That’s why the statement is true: ultrasonic frequencies have frequencies greater than 20 kHz. The other options describe frequencies outside the ultrasonic range—below 20 Hz would be infrasonic, and 1 to 2 Hz is far below human hearing as well—so they aren’t ultrasonic. In practice, ultrasound is used in applications like medical imaging and industrial testing precisely because its higher frequencies provide better resolution.