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A Wave travels

 
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Lost_student



Joined: 10 Apr 2011
Posts: 2
Location: Lost

PostPosted: Sun Apr 10, 2011 10:50 pm    Post subject: A Wave travels Reply with quote

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 Smile
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hepcj
Site Admin


Joined: 23 Jun 2007
Posts: 125

PostPosted: Mon Apr 11, 2011 10:59 am    Post subject: Reply with quote

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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