Propagation of sound
As light, sound travels in the form of wave. But sound waves travels or propagates in the form of longitudinal wave. In longitudinal wave the particles of a medium move to and fro along the direction of propagation of wave.
When the prongs of a tunning fork are vibrated by striking it on a soft pad, waves are produced which travel outwards through the air. When the prongs of the tunning fork move outwards, the air particles surrounding it are compressed i.e. the particles in the medium come close together. The region where the particles come close together is called compression. Similarly, when the prongs move imward, the air particles surrounding it move apart. This region where the particles move apart is called the rarefaction.
The regions of compressions have high pressure and that of racefactions have low pressure than normal. The direction of the compressions are along the wave motion and that of the rarefactions are opposite to it. In one complete vibration of prong there is one compression and one rarefaction. Such series of compressions and rarefactions are produced in the medium which constitute the sound waves.
In case of sound wave, the wavelength isw the distance between two consecutive compressions or rarefactions. One compression and one refrefaction forms one complete wave. As with other forms of wave motion, the following equation applies.
Wave velocity = frequency × wave length.
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