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प्रश्न
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उत्तर
The sound heard after reflection from a rigid obstacle (such as cliff, a hillside, a wall of a building, edge of a forest etc.), is called an echo.
Conditions necessary for echo formation are:
1. The minimum distance between the source of sound and its reflector should be 17 m.
2. Reflected sound should reach the person atleast 0.1 second after the original sound is heard.
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