The range of frequencies which a listener can distinguish is known as range of audibility. The audible range of sound for the human being is 20HZ to 20,000HZ. TheSound of frequency below 20 Hz is called infrasonic sound or subsonic sound and sound with frequencies above 20,000 Hz are known as ultrasonic or ultrasound.
Properties of ultrasonic or ultrasound
Applications of ultrasonic or ultrasound
Single sound of a certain pitch and duration made by a musical instrument or voice is called note. Notes may be similar or different from each other in three aspects. They are pitch, loudness (or intensity) and quality (or timbre).
Pitch is defined as the sharpness of sound. It depends only on the frequency of the sound vibrations.
Pitch depends on the following factor:
Intensity of sound is the quantity of sound energy per unit time flowing across unit area hold normally to the direction of propagation of sound waves.
∴ Intensity of sound =
To find the intensity at a distance ‘r’ from small source of sound ‘O’, we consider a sphere of radius r. If E is the sound energy passes through the surface area in the given time‘t’. Then,
∝ 1 ………………..(i)
If ‘a’ is the amplitude of the sound wave emitting from the source ‘O’. Then,
I ∝ a2 ……………….(ii)
From (i) and (ii), we get
a2∝ 1 / …………… (iii)
∴ a ∝ 1/r
The differences between intensity of sound and pitch of sound are as follows,
|Intensity of sound||Pitch of sound|
|It is related to the loudness of sound.||It is related to the sharpness of sound.|
|It depends on amplitude of sound wave.||It is depends on frequency of wave.|
|It is measurablequantity and its unit is decible.||It is not measurable quantity. It has no unit.|
Any four applications of ultrasound are as follows,
Pitch of sound dependson the following factors,
The factors on which the intensity or loudness of sound depends on are as follows,