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

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

Two musical notes of the same pitch and loudness are played on a violin and a piano. The waveforms are as shown in the figures below. Explain why the wave patterns are different.

The distance between two consecutive crests in a wave is known as:

Two astronauts cannot hear each other on the moon. Why?

Name three animals which can hear ultrasonic vibrations.