A student stands inside a long, empty corridor and claps once. He notices that when he is close to the far wall he does not hear any distinct echo, but after walking some distance away an echo becomes audible.
Answer the following questions based on this observation.
(i) Define an echo.
(ii) Explain why the human ear requires a minimum time gap of about 0.1s to perceive an echo as a sound separate from the original clap.
(iii) State any two factors that affect the speed of sound in air and briefly describe how each one influences the speed.