1 Introduction

Brownian motion is the simplest approximate way to treat the dynamics of non equilibrium systems.Thefundamental equation to describe the motion of a Brownian particle is Langevin equation which consists ofboth frictional and random forces.The fluctuation dissipation theorem relates these forces to each other.Insoft matter physics Brownian motion of colloidal particles opened a new era in the field of research.

When we consider Brownian particles, which are su�ciently small and light, in �uid then it will performrandom zig-zag motion. In that case the surrounding �uid exerts forces on Brownian particle whichare 'systematic' part and random

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