Sound - Introduction

Mechanical waves which can cause the sensation of hearing are called sound waves. These waves are produced by bodies vibrating at frequencies lying between the range of 20Hz and 20,000Hz, perceived by the human ear. This is known as the audible range of frequency. In terms of wavelength, this range extends from about 17m to 1.7cm. Mechanical waves of frequency lesser than 20Hz or greater than 20,000Hz are inaudible (i.e., cannot be heard by the human ear) and are respectively called infrasonics and ultrasonics. The seismic waves are infrasonic waves. Bats, dolphins and submarines make use of ultrasonics to find their way in the dark. The following are some of the properties of sound.

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Sound is caused by a body in vibratory motion

Sound is caused by a body in vibratory motion

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For example, an excited tuning fork or a plucked guitar string, produces sound. On close observation, the prongs of the tuning fork or the string is found to have a hazy and blurred outline on account of rapid vibrations. If they are gently touched with the fingers, a series of impulses will be felt. If a prong of a vibrating tuning fork is held against a suspended pith ball, the latter is pushed away from the prong, whenever it touches the prong. Again, the water in a beaker is violently agitated when the vibrating prongs are dipped into it. A small inverted v shaped paper rider placed on a string producing sound, is thrown off, indicating that it is in a state of vibration.