DP Physics (last assessment 2024)

Question 18N.3.HL.TZ0.16a

Date	November 2018	Marks available	[Maximum mark: 2]	Reference code	18N.3.HL.TZ0.16a
Level	HL	Paper	3	Time zone	TZ0
Command term	Determine	Question number	a	Adapted from	N/A

[Maximum mark: 2]

18N.3.HL.TZ0.16a

A beam of ultrasound of intensity I₀ enters a layer of muscle of thickness 4.1 cm.

The fraction of the intensity that is reflected at a boundary is

${\left( {\frac{{{Z_1} - {Z_2}}}{{{Z_1} + {Z_2}}}} \right)^2}$

where Z₁ and Z₂ are the acoustic impedances of the two media at the boundary. After travelling a distance x in a medium the intensity of ultrasound is reduced by a factor e^–μx where μ is the absorption coefficient.

The following data are available.

Acoustic impedance of muscle = 1.7 × 10⁶kg m^–2s^–1

Acoustic impedance of bone = 6.3 × 10⁶kg m^–2s^–1

Absorption coefficient of muscle = 23 m^–1

(a)

Determine, in terms of I₀, the intensity of ultrasound that is incident on the muscle–bone boundary.

[2]

Markscheme

I₀e^{−23 × 0.041}✔

= 0.39 I₀✔

Syllabus sections

Option C: Imaging

Option C: Imaging » Option C: Imaging (Additional higher level option topics) » C.4 – Medical imaging (HL only)

Option C: Imaging » Option C: Imaging (Additional higher level option topics)

Question 18N.3.HL.TZ0.16a

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