During a drama rehearsal, in an auditorium, Aftab shouted and heard a faint echo. On the day of the final event carpets, chairs with cushions and curtains were placed in the auditorium. The auditorium now had clear sound with no echo.

Answer the following :

(i) Why was an echo heard in the auditorium initially?

(ii) Why did echo disappear after adding of carpets, chairs with cushions and curtains ?

(iii) When is an echo heard ?

(iv) What is the minimum distance required for sound to travel to generate echo ?

(i) Initially, the auditorium had hard, bare surfaces like walls and floor, which are good reflectors of sound. So, the sound waves were reflected back, producing an echo.

(ii) Carpets, curtains, and cushioned chairs are soft and absorbent materials. They absorb sound waves instead of reflecting them, so the echo disappeared and the sound became clearer.

(iii) An echo is heard when the reflected sound reaches the ear after a sufficient time gap i.e., at least 0.1 s, so it is heard separately from the original sound.

(iv) The reflecting surface should be at least 16.5 m away from the source of sound. This allows the sound to travel about 33 m to and fro, producing a distinct echo.