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A-LevelPhysicsMedical physics9702/41 · Oct/Nov 2019 · Q94 Marks

Diagnosis using nuclear magnetic resonance imaging (NMRI) requires the use of a non-uniform magnetic field superimposed on a constant magnetic field of large magnitude. Explain the purpose of:

  1. (a)the large constant magnetic field[2]
  2. (b)the non-uniform magnetic field.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

  1. [B1] nuclei precess
  2. [B1] precession is about (direction of magnetic) field
  3. [B1] or frequency of precession is in radio-frequency range
  4. [B1] frequency (of precession) depends on field strength
  5. [B1] to locate/find position of (spinning) nuclei
  6. [B1] to change region where nuclei are detected

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About this question

Topic
Medical physics, A-Level Physics (syllabus 9702). Structured question, 4 marks.
Source
A-Level Physics, Oct/Nov 2019 Paper 4 Variant 1, question 9.

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