Short note on propagation of sound.( Sufficient for 5 marks in short points).

Sound is pictorially represented by a continuous succession of peaks and valleys. The distance between two consecutive peak or trough is termed as the wavelength of the wave or the period. The number of cycles per unit time is termed as the frequency of that sound. Frequency is measured in cycles per second, or Hertz. The faster an object vibrates, i.e. the higher the frequency, then the higher the pitch of the sound. The difference between a man’s voice and woman’s must be clearly evident to you. The voice of a man has a lower frequency which contributes to the deepness or the bass in the voice. Women, in contrast, have a voice with higher frequency resulting in a higher shrillness or pitch

Let an electric bell be enclosed within a bell jar which is placed over a disc. Through a hole in the disc, air can be removed by using a vacuum pump. On gradually removing the air, the sound of the bell becomes feebler and eventually becomes inaudible when all the air is removed from the tumbler. 

 If you hear a very loud sound, what do you do? You cover your ears. How do you think that helps? When you cover your ears, you shut off the air inside your ears from the rest of the atmosphere. The sound waves travelling around you are now unable to get through to your ear or the intensity of the sound you hear is greatly reduced. Your blocking your ears creates a discontinuity in the medium due to which the flow of sound energy is disturbed. Through this we can make a very important observation; Sound waves rely on the medium for propagation. The propagation of sound wave is not possible through vacuum. The medium here can be gas, liquid or solid. The speed of sound when it is travelling through a medium depends on the type of medium. The speed of sound when travelling through air is 343 m/s or 1,235 km/h.

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