# The effect of a given sound lasts on a human ear for about 0.1 second.Use this fact along with the knowledge of speed of sound to estimate the minimum distance of the reflecting object for getting a clear and a distinct echo?

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by kartikey1

2015-01-10T21:21:36+05:30

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Speed of sound = v = 340 meters /second  in air at normal temperature and weather conditions.

Suppose there is an object (like wall) that reflects sound nearby our ears.  We hear the sound directly from the source of sound and then also the reflected sound waves from the object (wall).  If the reflected sound comes to ear with in 0.1 second of the direct sound, then we cannot distinguish between them.

So the time difference between hearing of the sounds one directly and one reflected  - has to be at least  0.1 sec.

In this time duration  sound travels = 340 m/sec * 0.1 sec = 34 meters.

The MINIMUM distance of the reflecting wall from our ear = 34 / 2 = 17 meters.  Because sound travels to the wall and back to our ear.