CAIE A-Level Physics A2 24.1.6 I I0e X f…n Matter

[Maximum number: 4]

Ultrasound and X-rays are both types of wave that are used in medical diagnosis to form images of internal body structures.

(a)

For one type of wave passing through tissue, the wave has 72 % of its initial intensity after it has passed through 6.2 cm of the tissue.

Calculate the linear attenuation coefficient $\mu$ of the tissue for this wave.

\mu=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . \ldots . \ldots . \ldots . \ldots . . . . . . . . . . . . . . . ~ \mathrm{~cm}^{-1}

[ 2 ]

$I=I_{0} \exp (-\mu x)$ $\begin{aligned} \ln (0.72)=-6.2 \mu \mu=0.053 \mathrm{~cm}^{-1} \end{aligned}$

(b)

Another wave of the same type as in (b)(i) passes through 9.3 cm of the same tissue.

Calculate the percentage of the initial intensity of the wave that is attenuated by the tissue.

[ 2 ]

$I / I_{0}=\exp (-9.3 \times 0.053)$
( = 0.61)
percentage attenuated $=100 \times(1.00-0.61)$ $=39 \%$

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CAIE A-Level Physics A2 24.1.6 I I0e X for the Attenuation of Ultrasound in Matter Topic Practice

Question 1

Question (a)

Question (b)