Previous Year Question
Ultrasonics are sound waves of frequency
greater than 20,000 Hz
less than 10,000 Hz
equal to 1000 Hz
none of these
Correct Answer: A
Detailed Solution
The normal human ear can hear sound waves with frequencies ranging approximately from 20 Hz to 20,000 Hz (20 kHz). This range is known as the audible range.
Sound having a frequency greater than 20,000 Hz is called Ultrasonic sound or Ultrasound. Its frequency lies above the normal hearing limit of human beings, so it cannot normally be heard by humans.
Similarly, sound having a frequency below 20 Hz is called Infrasonic sound. Thus, the classification can be understood as:
Infrasonic: < 20 Hz → Audible: 20 Hz–20 kHz → Ultrasonic: > 20 kHz
Because of their high frequency, ultrasonic waves are used in applications such as medical ultrasonography, SONAR, detection of cracks in metal blocks and cleaning of components that are difficult to reach.