Question

15. Sounds having frequencies lower than 20 Hz are called (1)

A. Ultrasonic sound

B. Infrasonic sound

C. Audible sound

D. Periodic vibrations​

Answer 1

Answer:

infrasound

At the other end of the spectrum are very low-frequency sounds (below 20 Hz), known as infrasound

Answer 2

Answer:

b) infrasonic sound

Explanation:

the sound having frequency lower than 20hz is called infrasonic sound