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Question
What is the range of frequencies associated with (a) infrasound (b) audible sound, and (c) ultrasound ?
Solution
(a) Infrasonic sound refers to the sound having frequency lesser than 20 Hz. It is inaudible as its frequency lies below the human audible range of frequencies (20 Hz–20 kHz). These sounds are produced by objects vibrating very slowly. Whales and elephants can produce these sounds.
(b) Audible sounds include sounds of frequencies between 20 Hz and 20,000 Hz, which lies between the human audible range of frequencies.
(c) Ultrasonic sound refers to the sound having frequency higher than 20 kHz. It is inaudible as its frequency lies above the human audible range of frequencies (20 Hz–20 kHz). These sounds are produced by objects vibrating very rapidly. Bats and dolphins can produce these sounds.
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