Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

See the Brownian Motion

Objective

To observe the Brownian Motion.

Introduction

Brownian motion is a random movements performed by microscopic particles in a disperse phase e.g., particles in suspension in liquid or smoke particles in air. This motion is caused by the continuous irregular bombardment of the particles by the molecules of the surrounding medium.

Apparatus

transparent plane glass jar, torch, magnifying glass

Procedure

Take a transparent plane jar. Fill it with tap water completely and then cover it with a lid. Illuminate the jar from the sides using a torch. Tap water generally contains some suspended particles which scatter light and can be seen in the torch light beam. Use the magnifying glass to observe the suspended particles under illumination. When the water has become still, observe carefully and notice fluctuating small motion of particles (you will need patience to observe this). This will be more prominent for smaller particles.

Discussion

Brownian motion is caused by the unequal impact of molecules of water on the suspended particle from different sides.