4 Piezo-electric transducers are used for the generation of ultrasonic waves. (a) State one other use, apart from in ultrasound, of piezo-electric transducers. (b) Explain the main principles behind the use of ultrasound to obtain diagnostic information about internal body structures.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

1. [B1] e.g. microphone / weighing scales/pressure sensor / lighters/spark generation / watches/clocks/regulation of time
2. [B1] pulses (of ultrasound)
3. [B1] reflected at boundaries (between media)
4. [B1] (reflected pulses) detected by (ultrasound) generator
5. [B1] time delay (between transmission and receipt) gives information about depth (of boundary)
6. [B1] intensity of reflected pulse gives information about (nature of) boundary
7. [B1] gel used to minimise reflection at skin/maximise transmission into skin
8. [B1] degree of reflection depends upon impedances of two media (at boundary)