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Question
An echo will be heard if the minimum distance between the source of sound and the obstacle is :
[assume air to be the medium]
An echo will be heard if the minimum distance between the source of sound and the obstacle is :
[assume air to be the medium]
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Solution
The correct option is D 17m
As the sensation of sound persists in our brain for about 0.1 s, to hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1 s. If we take the speed of the sound to be 344 m/s at a given temperature, say at 22 0C in air, sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1 s.
Hence, the total distance covered by the sound from the point if generation tothe reflecting surface and back should be at least
344×0.1=34.4m.
Thus for hearing distinct echoes, the minimum distance pf the obstacle from the source of sound must be half this distance
That is, 34.42=17.2m≈17m
As the sensation of sound persists in our brain for about 0.1 s, to hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1 s. If we take the speed of the sound to be 344 m/s at a given temperature, say at 22 0C in air, sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1 s.
Hence, the total distance covered by the sound from the point if generation to
the reflecting surface and back should be at least
344×0.1=34.4m.
Thus for hearing distinct echoes, the minimum distance pf the obstacle from
the source of sound must be half this distance
That is, 34.42=17.2m≈17m
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