PHYSICS SEMINAR
DIFFUSION AND BROWNIAN MOTION
Andres F. Zambrano Moreno
Physics Department,
Bishop's University
Friday, February 4, 2011
1:30-2:30 p.m.
Nicolls 315
In this talk, some of the points discussed in the previous talk will be more thoroughly analysed. Starting with Fick's first law of diffusion, the diffusion equation will be derived along with a solution to this equation through Fourier transforms. This solution will later be identified with the diffusion coefficient D (which is a specific example of the fluctuation-dissipation theorem) obtained from the Langevin equation for Brownian motion and, through the use of Stokes' law, an expression for Avogadro's constant is obtained. Although the Einstein and Smoluchowski theories of Brownian motion look quite different (the former utilises statistical arguments while the latter uses a specific kinetic model), a link can be made between these two theories as proposed by P. Langevin. The idea behind this approach is to treat the forces felt by a suspended Brownian particle in a fluid as a sum of its average value and the fluctuations about this average.
