Sound Continuous disturbance that transfers energy without any net displacement of the medium particles is called wave. Different types of waves on the basis of their production are mechanical wave, electromagnetic wave and matter wave. Different types of mechanical waves on the basis of their propagation transverse wave and longitudinal waves. Mechanical waves need a medium for its propagation. Laws of reflections of sound: (i) The incident sound, the reflected sound, and the normal to the screen at the point of incidence all lie in the same plane. (ii) The angle of reflection of sound is always equal to the angle of incidence. Echo Reflection of sound Sensation of sound persists Minimum distance to hear echo in the human brain Reverberation Persistence of sound by repeated reflection Uses of Echo For determination of speed of sound: v = Total distance travelled by the soundTime interval in which echo reaches the place from where the sound t Bats and dolphins use echo to detect obstacle or enemy in their path Also, they use it to hunt their prey. Sonar is the acronym for SOund NAvigation and Ranging. It is an acoustic instrument installed in ships to measure depth, direction and speed of underwater objects such as icebergs, sea rocks, shipwrecks and spy submarines. It uses high-frequency ultrasound for this purpose and works on the principle of echo. In medical field: Here, echo method of ultrasonic waves is used to view human organs and any foreign body inside it. Natural vibrations The periodic vibrations of a body in the absence of any external force on the body are known as natural or free vibrations. The frequency of the body in natural vibrations is called its natural frequency.
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