1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Protein diffusion

  1. Apr 6, 2009 #1
    1. The problem statement, all variables and given/known data

    You release a billion protein molecules at position x=0 in the middle of a narrow capillary test tube. The molecues' diffusion constant is 10^-6 cm^2s^-1. An electric field pulls the molecules to the right (larger x) with a drift velocity of 1 micrometer per second. Nevertheless, after 80 s you see that a few protein molecules are actually to the left of where you released them. How could this happen? What is the ending number density right at x=0?

    2. Relevant equations

    Suppose N molecules all begin at the same location in 3D space at time zero. Later the concentration is

    [tex]
    c(r,t)=\frac{N}{(4 \pi Dt)^{3/2}} e^{-r^2/(4Dt)}
    [/tex]

    3. The attempt at a solution

    From a similar problem, it looks like the formula in 1D is

    [tex]
    c(r,t)=\frac{N}{(4 \pi Dt)^{1/2}} e^{-r^2/(4Dt)}
    [/tex]

    Is this correct?

    If so, we have

    [tex]
    c(0,80)=\frac{1 \cdot 10^9}{(4 \pi 1 \cdot 10^-6 \cdot 80)^{/2}} e^0 = 3.15E10 cm^-1

    [/tex]

    This clearly must be wrong, or what?
     
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted



Loading...
Similar Threads for Protein diffusion
Problem With Diffusion
Master equation -> diffusion equation