(a)[4]
Explain the physics behind the production of ultrasound waves used in medical diagnosis.
(b)[4]
A parallel beam of ultrasound waves in air has a linear attenuation (absorption) coefficient of $1.2\,\text{cm}^{-1}$. It travels through an air layer $3.5\,\text{cm}$ thick. Calculate the ratio, in dB, $\dfrac{\text{intensity of beam after passing through the layer of air}}{\text{intensity of beam entering the layer of air}}$.