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An ultrasound wave is incident normally on the boundary between two media. The media have specific acoustic impedances 
and 
. State how the ratio
depends on the relative magnitudes of and .
State what is meant by the attenuation of an ultrasound wave.
A parallel beam of ultrasound is passing through a medium. The incident intensity 
is reduced to 
on passing through a thickness of 
of the medium. Calculate the linear attenuation coefficient 
of the ultrasound beam in the medium.
.
