Sound Propagation
Dear students, we are already familiar with the types of waves. We know that there are two types of wave, viz. mechanical and electromagnetic waves. The waves which can travel through vacuum (or do not need medium for propagation) is known as electromagnetic wave and the waves which requires medium for the propagation of waves are known as mechanical waves. Most common example of mechanical wave is sound wave.
Sound wave can be explained with the help of an instrument known as tuning fork. Tuning fork is an instrument which has U shaped metal arms (prongs) fixed on base. When it strikes on rubber pad, sets in to vibrations which can illustrate is the propagation of sound.
When prongs of tuning forks vibrate outwards, particles of medium like air are crowded together and compression is formed, and when the prongs move backwards, particles found more space so that rarefaction is formed. The compression and rarefactions travels parallel to the vibrations of prongs of tuning fork. i.e. they forms longitudinal wave. These compression and rarefactions creates the reasons of high and low densities, which again creates the difference of pressure. The series of compression and rarefactions propagates in medium and sound is travels in medium. Compression is considered as a reason of high density and pressure whereas rarefactions are considered as reasons of low density of pressure. This change in pressure creates sensation on human ear and one can listen the sound. This indicates that the propagation of sound wave is nothing but a longitudinal wave. The same can be experienced when the bell in temple is strike to produce sound.