what is an echo? what are the two conditions required to hear an echo?
Echo : An echo can be defined as the phenomena of the reflection of sound produced by a source placed in a relatively open environment after it hits a distant obstacle like a cliff etc. The sound waves that have bounced back can be heard at the source a few seconds after it was produced.
(1) The echo must reach our ears atleast after 1/10 seconds we hear the original sound, otherwise we will not be able to distinguish it from the original sound as a sound stays ( persists) in our brain for about 1/10 of a second ( persistence of sound).
(2) The source of sound and the reflecting surface should be atleast 17 m apart for us to hear the echo.
if sound is reflectad back from an obstacle to the listener in such a way that he listens it distinctly as a repetation of the original sound is called an echo.the two conditions are
1) it should reach the person after 1/10th of a second and
2)the minimum distance must be 54ft or 16.5 m