Name: Introduction to Brownian Motion
Uploaded: 2019-07-19
Duration: 3 min 35 s
Description: The study of Brownian motion is important in the study of the kinetic theory of gases. But what is meant by the Brownian motion? Let's understand it in this...

Question

How Brownian motion could be explained on the basis of thermal motion of the molecules?

Accepted Answer

The liquid molecules during their chaotic thermal motions collide with the suspended particles. If the sizes of the suspended particles are very large compared to the molecules, large number of molecules from all sides collide with the suspended particle. So the suspended particle does not feel any net force. But if the size of the particle is not so large Radius of the particle is between $10^{- 3}$ to $10^{- 5}$ Cm, then number of molecules striking the particle from all sides are, by law of chance, not equal. Hence, they feel a net impulse at each instant. As a result, they move continuously. The thermal motions of the liquid molecules are absolutely chaotic, Therefore the magnitudes and directions of the net impulses experienced by the suspended particles are also absolutely random. We cannot see the molecules, but we can see their effects in the Brownian motion of the suspended particles.

Einstein by elaborate calculations predicted some behaviour of the suspended particles. These predictions were confirmed by experiments done by Perrin. From these experiments Avogadro number was also determined. The success of Einstein's Theory of Brownian motion had a large impact on notions of scientists at that time. Many believed at that no fruitful explanation of big bodies could be achieved by considerations of motions of the atoms and molecules. They had to abandon their scepticism.

How Brownian motion could be explained on the basis of thermal motion of the molecules?

Important Questions on Kinetic Theory of Gases

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