(a(i))[2]
State what the specific acoustic impedance of a medium means.
(a(ii))[2]
The intensity reflection coefficient $\alpha$ is expressed by $\alpha = \dfrac{(Z_2 - Z_1)^2}{(Z_2 + Z_1)^2}$. Explain what each symbol in this expression represents.
(b)[5]
A parallel ultrasound beam has intensity $I_0$ when it enters muscle. It then travels through $3.4\,\text{cm}$ of muscle before reaching the boundary with bone, as shown in Fig. 4.1. The intensity of the ultrasound beam after entering the bone is $I_T$. Calculate the ratio $\frac{I_T}{I_0}$.