On which day, a hot day or a cold day, an echo is heard sooner? (Give reason for your answer.

What name is given to sound waves of frequencies higher than 20 kHz?

Fill in the following blanks with suitable words:

(a) An echo is simply a ………. Sound.

(b) Pitch od sound depends on ………

(c) Loudness of sound depends on ……….

(d) Quality of sound depends on ……….

(e) Echoes are caused by the …………of sound.

In which medium, air or water, an echo is heard much sooner? Why?

What is reverberation? What will happen if the reverberation time in a big hall is too long?