Propagation of Sound
A material medium is necessary for the propagation of sound. Sound can travel through solids, liquids and gases, but not through vacuum. During the propagation of sound, the particles of the medium do not travel, only the energy is being transferred from one particle to another.
Sound gets reflected when it travels in a medium. Like light, it also follows the laws of reflection. The repetition of sound caused by the reflection of sound waves by a tall building or a mountain is known as echo. The time interval between the original sound and reflected one should be at least 0.1 s in order to hear a distinct sound. However, the persistence of sound due to the repeated reflections of sound is known as reverberation. Reflection of sound is used by animals such as bats and dolphins to locate their prey. It is also be used to find the depth of the sea using an instrument called SONAR.
Human beings and most of the animals are able to hear with the help of a sense organ, called the ear. It consists of three basic parts - outer ear, middle ear and inner ear. Ears convert pressure variations in air with audible frequencies into electric signals that travel to brain via auditory nerve.
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