Explain the principles of the detection of ultrasound waves for medical diagnosis.

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

1. [1] pulses of ultrasound
2. [1] ultrasound incident on quartz crystal
3. [1] waves make crystal oscillate
4. [1] oscillations (of crystal) generates an e.m.f. (across the crystal)
5. [1] specific acoustic impedances of air and skin are very different
6. [1] intensity reflection coefficient depends on difference between acoustic impedance
7. [1] most ultrasound reflected so little transmission