What is the minimum distance (in metres ) required to hear an echo ?

Options

A. 10
B. 13
C. 17
D. 21

Answer

3

Explanation

The human ear cannot distinguish echo from the original direct sound if the delay is less than `1//15` of a second. The velocity of sound in dry air is approximately 343m`//` s at a temperature of `25^(@)C`. Therefore, the reflecting object must be more than 17.2m from the sound source for echo to be perceived by a person located at the source.