What is meant by aan echo ? Explain.

Explanation

Echo: An echo is a repetition of sound produced by the reflection of sound waves from a wall, mountain or other obstructing surfaces.
Explalation : The speed of sound in air at `20^(@) C ` is `344 ms^(-1)` If we shout at a wall which is at 344 m away, then the sound will take 1 second to reach the wall. After reflection, the sound will take one more second to reach us. Therefore, we hear the echo after two seconds. Scientists have estimated that we can hear two sounds properly if the time gap or time interval between each sound is `((1)/(10))^(th)` of a second (persistence of hearing ) i.e. , 0.1 s . Then , Velocity = `("Distance travelled")/("Time taken") = (2d)/(t)`
`2d = 344 xx 0.1 = 34.4 m , d = 17.2` m
The minimum distance from a sound reflecting wall to hear an echo at `20^(@)C ` is 17.2 meter