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Lost_student
Joined: 10 Apr 2011 Posts: 2 Location: Lost

Posted: Sun Apr 10, 2011 10:50 pm Post subject: A Wave travels 


Can someone help me with this problem I cant seem to make heads or tails of it. This question came from the Biological Physics book
A wave travels from air (Zair = 413 kgm−2 s−1) into a liquid and with a density of 950 kg m−3 and in
which the speed of sound is 750ms−1.
(a) What proportion of the wave is reflected from the boundary?
(b) What proportion of the wave is transmitted through the boundary?
Many thanks in return for your help 

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hepcj Site Admin
Joined: 23 Jun 2007 Posts: 125

Posted: Mon Apr 11, 2011 10:59 am Post subject: 


First you need to work out the acoustic impedance of water which is the density x the speed of sound.
Z_liquid = p_liquid x v_liquid = 712500 kg m^2 s^1
a) The reflection coefficient is then (Z_liquid  Z_air)/(Z_liquid + Z_air) = 0.998841
so about 99.8% of the sound wave is reflected.
b) The transmission coefficient is 2Z_air/(Z_liquid + Z_air) = 0.00116
or 0.12% is transmitted. 

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