At 20°C, the minimum distance of a person from a sound reflecting surface to hear an echo is :

A. 12.2 m B. 17.2 m

C. 15.2 m D. 34.4 m

(a) What is an echo?

(b) How is an echo different from a reverberation?

(c) Describe an activity to demonstrate that sound follows the same laws of reflection as light.

Describe two uses of multiple reflections of sound.

Shirin went to an opera house. She appreciated its architecture and furnishing. The curved ceiling draperies, cushions and curtains were perfectly placed. She also saw sound board behind the stage. She now wondered if each of these accessories were placed for the sake aesthetics of the hall or had a scientific reason too.

(a) What is the purpose of curtains, cushions and draperies in an opera house?

(b) How des curved ceiling and sound board help?

(c) List some characteristic qualities of Shirin.

Aditi clapped her hands near a cliff and heard the echo after 4 seconds. What is the distance of the cliff her if the speed of sound is taken as 346 ms^-1.

Define reverberation.

An echo is returned in 6 seconds. What is the distance of reflecting surface from source? [given that speed of sound is 342 m/s.]

What is a stethoscope? Name the principle on which a stethoscope works.