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  Physics (NTSE/Olympiad)  

5. Sound

Introduction to Sound

Sound is a form of energy that produces the sensation of hearing in our ears.
Frequency range of audible sound for human is between 20Hz to 20 KHz
Sound need Material to Travel : You have learnt in previous section that vibrations produce sound. To produce vibrations, we need a material body. Therefore, we can say that a medium is needed for sound to travel. Sound can travel through air (or gases), liquids and solids, but not through vacuum.
Speed of Sound :The speed of sound is the rate at which sound travels from the sound producing body of our ears. The speed of sound depends on the
(i) Nature of Material (or medium) through which it travels. Speed of sound in air is 344 m/s.
(ii) Temperature : As the temperature increases the speed of sound in air increases.
(iii) Humidity of Air : Sound travel first in humid air.
The Time Gap between 'Seeing' and 'Hearing' is due to the difference between the time taken by the light and the sound to travel from the source to the observer.
The speed of light high 3 × 108 meters per second (30 crore metres per second) and the speed of sound in the air under normal conditions is 344 metres per second. So, the light travels almost instantaneously, whereas sound takes some time.
Sound Wave are Longitudinal Waves : Sound travels through air in the form of longitudinal waves.

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