# Another diffusion problem

Discussion in 'General Science' started by boks, Jan 25, 2009.

1. ### boks Thread Starter Active Member

Oct 10, 2008
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Calculate the diameter of a spherical particle (r = 4 g·cm-3) for which the root mean square (rms) displacement due to diffusion is 1% the distance of sedimentation in 24-hr period. The temperature is 25°C. The continuous phase has a density of 1 g·cm-3 and viscosity of 0,9 mPa·s.

For what diameter is the diffusion distance 10% of the settling distance?

I know that $\bar{x}^2 = 2Dt$, but I'm unsure how to find D.