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Conceptual question about longitudinal waves 
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#1
Oct1207, 10:26 PM

P: 3,015

So we are working on sound waves in my physics course now and I was doing some textbook reading. I have been following it pretty well, but I just came across a relationship that I am not quite following.
It is with reference to wave interference. Let us say that two sound waves are emitted from two different point sources [tex]S_1[/tex] and [tex]S_2[/tex]. The waves have the same wavelength [tex]\lambda[/tex] and are in phase at their sources. They take paths of lengths [tex]L_1[/tex] and [tex]L_2[/tex] and pass through point P. The text says that their phase difference [tex]\phi[/tex] is dependent on [tex]\Delta L=L_1L_2[/tex] Thus to relate the variables [tex]\Delta L[/tex] and [tex]\phi[/tex] we can use the proportion: [tex]\frac{\phi}{2\pi}=\frac{\Delta L}{\lambda}[/tex] I know that I should see it, but I don't exactly follow this proportion. Could somebody ellaborate on this a little for me? I sure would appreciate, Casey 


#2
Oct1207, 11:59 PM

HW Helper
P: 4,124

Suppose the equation of both waves is: y = Acos(kx) (going along the direction the wave is travelling)
The wavelength of this wave is 2*pi/k So at the point of interest, suppose wave 1 has travelled L1, and wave 2 has travelled L2: y1 = Acos(kL1) y2 = Acos(kL2) the phase of the first wave is kL1. the phase of the second is kL2. phase difference is: kL1  kL2 = [2*pi/wavelength]*(L1  L2) so from this we get the phase difference relationship. 


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