. What are ultrasonic waves
A: Sound waves having frequency shorter than audio frequency range
B: Sound waves produced in a vaccum
C: Sound waves having frequency higher than audio - frequency range
D: None of these
The audible frequency range for the human ear is 20Hz to 20000Hz; sound waves over 20000Hz are ultrasonic, while sound waves below 20Hz are infrasonic.
Ultrasonic waves are defined as sound waves with a frequency greater than the audio frequency range (20.000Hz).
Hence, option C is correct, i.e., Sound waves having frequency higher than audio - frequency range.