Flux density help please (seawater flowing in a tube)

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The discussion focuses on calculating the flux density of salt in a tube connecting seawater and freshwater, emphasizing that the question lacks sufficient data for a definitive answer. Participants highlight the importance of considering diffusion coefficients and the limitations of using velocity and concentration due to the absence of advection. Dimensional analysis is mentioned as a method to argue the problem's complexity. Clarification is sought regarding whether tabulated values can be utilized in the calculations. Overall, the conversation underscores the need for more information to accurately determine the flux density.
olibee
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Homework Statement
this is a practice problem set
Relevant Equations
I know flux = concentration x velocity but I am not quite understanding if that is applicable here
What is the flux density of salt in a horizontal tube 10 cm in length connecting seawater (salinity = 30 g/l) to a tank of freshwater (salinity ~ 0) assuming no advection occurs?
 
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An answer cannot be given based on only the data you have given. This is easy to argue with dimensional analysis. Is this the full question as stated? Are you allowed to look up tabulated values such as the diffusion coefficient of salt in water?
 
And you are right. Velocity * concentration does not apply because that is based on an advective flux and it is explicitly stated that there is no advection.
 
Thread 'Correct statement about size of wire to produce larger extension'

Thread 'Correct statement about size of wire to produce larger extension'

The answer is (B) but I don't really understand why. Based on formula of Young Modulus: $$x=\frac{FL}{AE}$$ The second wire made of the same material so it means they have same Young Modulus. Larger extension means larger value of ##x## so to get larger value of ##x## we can increase ##F## and ##L## and decrease ##A## I am not sure whether there is change in ##F## for first and second wire so I will just assume ##F## does not change. It leaves (B) and (C) as possible options so why is (C)...
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