Question

Sounds having frequency more than $20000\,Hz$ are called
(A) sonic sound
(B) ultrasonic sound
(C) infrasonic sound
(D) none of these

Answer 1

Hint: Sound propagates through the medium as an acoustic wave. The audible range of the sound that the human can hear is from $20\,Hz$ to $20000\,Hz$. Humans cannot hear the sounds that lie above $20000\,Hz$ or below $20\,Hz$. But some of the animals and birds can hear the sounds that are less or greater than the limit.

Complete step by step solution:
Sound is the vibration that transmits through any medium like gas, liquid or solid. Sound is classified into two types. Audible sound and inaudible sound. The audible sound lies in the range $20\,Hz$ to $20000\,Hz$. Inaudible sound is of two types, infrasonic sound and ultrasonic sound. Infrasonic sounds are the low frequency sound that lies below $20\,Hz$. Animals like rhinos, elephants, pigeons, octopus, cod etc can hear infrasonic sound.
Ultrasonic sounds are very high pitched. These sounds have the frequency above $20000\,Hz$. Animals like dogs, cats, bats and dolphins can hear these sounds. Rats communicate with the other rats using ultrasonic sounds. Bats catch their prey using these waves. Bats send ultrasonic waves with the high frequency of $20\,KHz$ to $100\,KHz$ and using echolocation it senses at what distance the prey is. Dolphins also use this technique to find its prey inside the water. Hence the sound range above $20000\,Hz$ is called ultrasonic sound.

Thus, option (B) is correct.

Additional information:
The sounds that are unpleasant to hear are called noise. Frequency is also known as pitch which is the number of times that the sound wave repeats per second.

Note: Ability to detect the objects or animals location by sensing the echoes emitted from them is called echolocation. It is also known as a biological sensor. Frequency of sound is measured in $Hz$.