If the density of a medium through which sound is propagating is minimum,then this point is called:

State four differences between longitudinal and transverse waves. Give an example of each.

The speed of sound is $310 \, m s^{-1}$. $A$ person fires a gun and the echo is heard after $1.5 \, s$. Calculate the distance of the person from the cliff from which the echo takes place. (in $, m$)

How does the sound produced by a musical instrument reach your ears? Astronauts need radio transmitters to talk to each other on the moon. Why?

$(a)$ What is the cause of the sensation of sound due to the rolling of thunder?
$(b)$ Give the audible range of the human ear.
$(c)$ What are infrasonic and ultrasonic waves?

If $20$ waves are produced per second,what is the frequency in hertz (in $, Hz$)?