The bells of a temple are made of large size. It is for

$(a)$ Mention two practical applications of reflection of sound waves.
$(b)$ How is the pressure variation in a sound wave amplified in the human ear?
$(c)$ In a ripple tank,$10$ ripples are produced per second. If the distance between a trough and a neighbouring crest is $12 \, cm$,calculate the frequency,wavelength,and velocity of the wave.

$(a)$ Illustrate the use of a stethoscope.
$(b)$ What are infrasonic and ultrasonic sound waves?

Why can we hear echoes in long galleries and big halls?

The pulse rate of a man is $80$ beats in one minute. Calculate its frequency. (in $ Hz$)

Sound travels in air if