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Question
At 20oC,the minimum distance of a person from a sound reflecting surface to hear an echo is.
At 20oC,the minimum distance of a person from a sound reflecting surface to hear an echo is.
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Solution
The correct option is C 17.2m
Answer is C.
The sensation of sound persists in our brain for about 0.1 s. That is, to a hear a distinct echo the minimum time interval between the original sound and the reflected sound = 0.1 s.
Speed of sound in air, at a given temperature, say 20 degrees C = 344 m/s.
Here, the 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 of generation to the reflecting surface and back = 344 * 0.1 = 34.4 m.
Thus, for hearing the echo, the minimum distance of the obstacle from the source of sound must be half of this distance. That is, 17.2 m.
Answer is C.
The sensation of sound persists in our brain for about 0.1 s. That is, to a hear a distinct echo the minimum time interval between the original sound and the reflected sound = 0.1 s.
Speed of sound in air, at a given temperature, say 20 degrees C = 344 m/s.
Here, the 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 of generation to the reflecting surface and back = 344 * 0.1 = 34.4 m.
Thus, for hearing the echo, the minimum distance of the obstacle from the source of sound must be half of this distance. That is, 17.2 m.
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