A boy stands at a distance from a tall brick wall in an open field and claps his hands loudly. Answer the following questions based on this situation.
(i) Define an echo.
(ii) The boy hears the echo of his clap 2.4s after he produces the sound. Explain why the distance between the boy and the wall is equal to 2vt, where v is the speed of sound in air and t is the measured time interval.