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प्रश्न
Why is an echo not heard when the distance between the source of sound and reflection body is less than 10 m?
उत्तर
The impression of sound lasts on the eardrum for `1/10` of a second. In `1/10` of a second, the sound travels a distance `332"m"/"s"xx1/10"s"` = 33.2. Thus, the minimum distance between the source of the sound and the reflecting body should be `33.2/2` = 16.6 m.
As the distance 10 m is far less than 16.6 m, therefore the ear cannot make out when the original sound had died and echo has been received. Thus, no echo is heard.
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