Chapter 17, Problem 41A

To determine

To explain: The reason for the apparent nature of Brownian motion only for microscopic particles.

Explanation of Solution

Introduction:

The first experimental evidence that matter consist of tiny particle in motion was given by the Robert Brown. He observed the motion of very small pollen grains suspended in water using very high power microscope. The suspended particles were seen to move completely haphazardly and execute perpetual movement. This irregular motion of the particles is termed Brownian motion.

Brownian motion is apparent only for microscopic particles. When small particles are suspended in a solution, then these particles gets hit by less number of molecules. Also, they are not hit equally from all sides, due to which a resultant force will occur that alter the direction of particles. When particles move, then resultant force direction will change causing zigzag motion. But this is not possible in case of large particles. This is because when an isolated large particle suspended in a solution, a number of molecules will hit particle from all sides. So, the impact will mutually cancel out and the resultant force on the particles is zero.

Conclusion:

Therefore, Brownian motion is apparent only for microscopic particles not for large particle.