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## Homework Statement

Imagine a narrow pipe, filled with fluid, in which the concentration of a certain type of molecule varies only along the length of the pipe (in the x direction). By considering the flux of these particles from both directions into a short segment [tex]\Delta[/tex]x, derive Fick's second law, dn/dt = D d

^{2}n/dx

^{2}(those should be partial derivatives not normal ones) where n is the particle concentration and D is the diffusion coefficient.

## Homework Equations

J

_{x}= -D dn/dx

where J is the particle flux

## The Attempt at a Solution

I don't even know where to start