2003/03/16 by Kasturi Basu, Kopinjol Baishya
Physics and Astronomy · #physics.ed-ph
published as Resonance Vol. 8, No. 3, 71-80, March 2003 · 5 pages, 4 figures
arxiv created 2003/03/16 · arxiv updated 2009/12/01
Brownian motion is the perpetual irregular motion exhibited by small particles immersed in a fluid. Such random motion of the particles is produced by statistical fluctuations in the collisions they suffer with the molecules of the surrounding fluid. Brownian motion of particles in a fluid (like milk particles in water) can be observed under a microscope. Here we describe a simple experimental set-up to observe Brownian motion and a method of determining the diffusion coefficient of the Brownian particles, based on a theory due to Smoluchowski. While looking through the microscope we focus attention on a fixed small volume, and record the number of particles that are trapped in that volume, at regular intervals of time. This gives us a time-series data, which is enough to determine the diffusion coefficient of the particles to a good degree of accuracy.