Hertz is a unit of

$A$ hospital uses an ultrasonic scanner to locate tumours in a tissue. What is the wavelength of sound in a tissue in which the speed of sound is $1.7 \, km \, s^{-1}$? The operating frequency of the scanner is $4.2 \, MHz$ $(1 \, MHz = 10^{6} \, Hz)$.

What do you understand by the term infrasonic vibrations?

When we change a feeble sound to a loud sound,we increase its:

$(a)$ 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?

Establish the relationship between the speed of sound, its wavelength, and frequency. If the velocity of sound in air is $340 \, m \, s^{-1}$, calculate:
$(i)$ The wavelength when the frequency is $256 \, Hz$.
$(ii)$ The frequency when the wavelength is $0.85 \, m$.