Physics
Answer
(i) The sound heard after reflection from a distinct obstacle (such as a cliff, a hillside etc.) after the original sound has ceased is called an echo.
(ii) Conditions for an echo to take place are :
- The size of the reflector must be large enough as compared to the wavelength of the sound wave.
- The intensity of sound should be such that the reflected sound reaching the ear is sufficiently loud to be audible.
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