What are Ultrasonic waves?
(A) Sound waves having frequency shorter than audio frequency range
(B) Sound waves produced in a vacuum
(C) sound waves having frequency higher than audio frequency range
(D) None of these

Hint: To answer this question, we need to use the audible frequency range, which the human ears are capable of hearing. Then, focusing on the meaning of the term “ultra”, we can answer this question.

Complete step-by-step answer The terms ultrasonic and infra-sonic are used in reference to the audio frequency range which the human ear is capable of hearing. We know that this audio frequency range is from \[20Hz\] to \[20KHz\] or \[20000Hz\].
As the name suggests, the term ultrasonic waves means the sound waves of frequency higher than this range and the term infra-sonic waves means the sound waves of frequency lower than this range. So the infrasonic waves are the sound waves having frequency less than \[20Hz\] and the ultrasonic waves are the sound waves having frequency more than \[20000Hz\].

Hence, the correct answer is option C, sound waves having frequency higher than audio frequency range.

Note: The ultrasonic waves are the sound waves which are beyond the frequency range of hearing, that’s why they have the name ultrasonic. Due to the high frequency possessed by them, they are highly energetic waves. They can be transmitted over long distances without the loss of energy. They have various applications for different purposes as listed below:
1. Communication – Due to their high energy, they are transmitted over long distances and are used for communication purposes.
2. Sonar – The ultrasonic waves are used to detect objects under the water. This technique is known as SONAR (sound navigation and radiation).
3. Machining of hard materials – As they are highly energetic, they can be used to cut the hard materials.
4. Ultrasound – They can propagate through the human body to take the image of the internal organs of the body.