Question

The sounds having frequency less than $20Hz$ are called ultrasonic. True or False?

Answer 1

Hint
We should know that in physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Sound waves below 20 Hz are known as infrasound. Noise is an unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, noise is indistinguishable from sound, as both are vibrations through a medium, such as air or water. Acoustic noise is any sound in the acoustic domain, either deliberate (e.g., music or speech) or unintended.

Complete step by step answer
The sounds having frequency less than $20 \mathrm{Hz} 20 \mathrm{Hz}$ are called infrasonic. The sounds having frequency greater than $20 \mathrm{kHz}$ are called ultrasonic. Human beings can hear only those sounds which are in the frequency range of $20 \mathrm{Hz}$ to $20 \mathrm{kHz}$. Thus, the infrasonic and ultrasonic sounds are not audible to humans.
Therefore, the given statement is False.

Note
It is to be known for our knowledge that the term ultrasonic applied to sound refers to anything above the frequencies of audible sound, and nominally includes anything over 20,000 Hz. Frequencies used for medical diagnostic ultrasound scans extend to 10 MHz and beyond. Ultrasound is a very high-pitched sound. We cannot hear ultrasound; it has a frequency above 20,000 Hz, the upper limit of human hearing. However, animals, such as dogs, bats, and dolphins, can hear these very high-pitched sounds. Although Ultrasound cannot be heard by humans, at high decibels it can still cause direct damage to human ears. Ultrasound in excess of 120 decibels may cause Hearing damage. Exposure to 155 decibels causes heat levels that are harmful to the body. 180 decibels may even cause death.