Ultrasound is used to produce diagnostic information about internal body structures.
Explain how ultrasound waves are detected.
An alternating voltage 
varies with time 
according to
The voltage is applied to an ultrasound probe. The root-mean-square (r.m.s.) voltage is 
. The frequency of the ultrasound generated by the probe is 
. Determine the values of
The table below contains information about air and soft tissue.
Determine the unit for the specific acoustic impedance values shown in the table.
Calculate the density of soft tissue.
Use data from the table to explain why ultrasound cannot be used to produce an image inside an air-filled cavity such as the lungs
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