The production of an Echo is a common example of reflection of sound.An echo is the repetition of sound caused by its reflection from a distant surface.

A human ear cannot distinguish between two sounds if they are heard within an interval of 1/10 of a second.Therefore echo can be heard only if the reflected sound reaches the ear at least 1/10 of a second after the direct sound is heard.The velocity of sound in air at ordinary temperature is about 340 m/s.It is obvious that the sound should reach the ears after it covers a minimum distance of 340 X 1/10 = 34 Metre.In other words echo is heard only if the reflecting surface is at a distance greater than 17 Metre.

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