(a) Explain the main principles behind the use of ultrasound to obtain diagnostic information about internal body structures.
(b) (i) Define specific acoustic impedance.
(ii) Two media have specific acoustic impedances of Z₁ and Z₂.
The magnitudes of the acoustic impedances may be almost equal or very different.
State how these differences affect the intensity reflection coefficient at the boundary between the two media.
Z₁ ≈ Z₂
Z₁ » Z₂ or Z₁ « Z₂

Q: What topic does this question test?

This question tests Medical physics in A-Level Physics (syllabus code 9702). It is worth 10 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Physics Feb/Mar 2018 examination, Paper 4 Variant 2 (9702_m18_qp_42.pdf).

Question

(a) Explain the main principles behind the use of ultrasound to obtain diagnostic information about internal body structures.
(b) (i) Define specific acoustic impedance.
(ii) Two media have specific acoustic impedances of Z₁ and Z₂.
The magnitudes of the acoustic impedances may be almost equal or very different.
State how these differences affect the intensity reflection coefficient at the boundary between the two media.
Z₁ ≈ Z₂
Z₁ » Z₂ or Z₁ « Z₂

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