Question

Define Brownian motion.

Answer 1

Brownian motion:

1. An English Botanist, Robert Brown 1827 found the best evidence for the existence and motion of particles in liquids.
2. Under the microscope he observed a continuous and rapid zig-zag motion in colloidal solution. he called this continuous and rapid zig-zag motion of the colloidal particles as Brownian motion.
3. This motion is independent of the nature of the colloidal particles.
4. It is more rapid when the size of the particles is small and the solution is less viscous.
5. The Brownian motion is due to the bombardment of colloidal particles by molecules of the dispersion medium.
6. The intensity of motion depends upon the size of the particles and the viscosity of the dispersion medium.
7. The smaller the particles and the less viscous the dispersion medium, the more vigorous is the Brownian motion and vice versa.

The figure of Brownian motion in colloidal solution as observed through the microscope: