A medical practitioner uses an ultrasound transducer to estimate the depth of a patient's kidney tissue interface.
Ultrasound pulses are emitted into the patient's body. Some of these waves are reflected at tissue boundaries and detected by the transducer.
The shortest time between the ultrasound pulse being emitted and the reflected echo being detected is 50 μs50\,\mu\text{s}50μs (where 1 μs=10−6 s1\,\mu\text{s} = 10^{-6}\text{ s}1μs=10−6 s).
The average speed of ultrasound in the human soft tissue is 1540 m/s1540\text{ m/s}1540 m/s.
Calculate the distance from the transducer to the nearest point on the kidney tissue interface. Give your answer in millimetres.
Each ultrasound pulse is emitted for a very short duration.
The reflected wave signal received back at the transducer is detected over a longer duration than the emitted pulse.
Suggest two reasons for this difference in duration.