Question

3.
Sound waves with a frequency below 20 Hz are called
(a) Infrasonic waves
(b) Ultrasonic waves
(c) Ultrasound
(d) None of these​

Answer 1

none of these is the answer

Answer 2

option A)Infrasonic waves

Explanation:-

Sound waves are categorized on the basis of their frequency range.

Sound of frequency below 20 Hz is called as infrasonic. Sound of frequency above 20 kHz is called as ultrasonic whereas sound of frequency in between 20 Hz to 20 kHz is called as audio sound.

Hope my answer helps you :))