Physics 9702 · AS & A Level · Production and use of ultrasound

Production and use of ultrasound — practice question

Table 8.1 presents some data about the properties of air, gel and body tissue. The data are given to three significant figures.
(a(i))[1]

Demonstrate that the specific acoustic impedance of gel is $1.68 \times 10^{6}\,\text{kg m}^{-2}\,\text{s}^{-1}$.

(a(ii))[2]

Complete Table 8.1 by finding the missing values to three significant figures. Use the space below for any working you need.

(b(i))[2]

Using the information in (a), calculate the intensity reflection coefficient for an air-tissue boundary.

(b(ii))[1]

Using the information in (a), calculate the intensity reflection coefficient for a gel-tissue boundary.

(c)[2]

Use your answers in (b) to explain why gel is placed on the skin during ultrasound scanning.

Worked solution & mark scheme

This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: specific acoustic impedance can be written as $Z = 1200\times1400 = 1.68\times10^6\,\mathrm{kg\,m^{-2}\,s^{-1}}$

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