Physics 9702 · AS & A Level · Production and use of ultrasound
Production and use of ultrasound — practice question
A parallel ultrasound beam is normally incident on the surface of a fat layer with thickness $1.1\,\text{cm}$, as illustrated in Fig. 6.1. For the ultrasound, $I_1$ denotes the intensity immediately after the wave enters the fat surface, $I_2$ denotes the intensity incident on the fat-muscle boundary, $I_3$ denotes the intensity reflected from the fat-muscle boundary, and $I_4$ denotes the intensity that returns to the fat surface. Some data for the fat are shown in Fig. 6.2.
(a)[3]
Calculate the time taken between a short pulse of ultrasound first entering the fat layer and then arriving back at the surface of the fat layer.
(b)[2]
Calculate the ratio $\frac{I_2}{I_1}$.
(c)[2]
Intensity $I_4$ is $0.33\%$ of intensity $I_1$. Determine the ratio $\frac{I_3}{I_2}$.
(d)[1]
The specific acoustic impedance of the muscle is greater than that of the fat. State the effect, if any, on the value of the ratio $\frac{I_3}{I_2}$ when the difference between the specific acoustic impedance of the muscle and that of the fat increases.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Application of $v=2f/p$” …