(a)[2]
State the meaning of the specific acoustic impedance of a medium.
(b)[2]
A parallel beam of ultrasound with intensity $I_0$ is incident on the boundary between two media A and B, as shown in Fig. 4.1. Media A and B have specific acoustic impedances $Z_A$ and $Z_B$ respectively. The intensity of the beam that passes through the boundary is $I_T$. State how the ratio $\frac{\text{intensity } I_T \text{ of transmitted beam}}{\text{intensity } I_0 \text{ of incident beam}}$ depends on the relative magnitudes of $Z_A$ and $Z_B$.
(c)[3]
The linear absorption (attenuation) coefficient $\mu$ of medium B is $23\,\text{m}^{-1}$. Calculate the thickness of medium B needed to cut the ultrasound beam intensity down to $34\%$ of its initial value in medium B.