The time, size, viscosity, and temperature dependence of the Brownian motion of polystyrene microspheres

An upper division undergraduate laboratory module to study Brownian motion was developed using polystyrene microspheres suspended in a sample liquid cell that was isolated from its surroundings. The dependence of the Brownian motion of the microspheres on their radius, the time, the viscosity of the suspension liquid, and the temperature were measured using a CCD camera interfaced witha frame grabber and a computer. The motion of each particle was monitored for 5 minutes and was found to be consistent with the Langevin formula for Brownian motion. (C) 2007 American Association of Physics Teachers.