oct_25.txt

Roll No: 2020101058
Date: 25/10/2021  
Important keywords mentioned in today's lecture

1. Brownian motion
2. Fluctuation dissipation theorem
3. Light gas
4. Light according to plank
5. Ensembles

My understanding of these keywords is:

1. Brownian motion:-
    - Particles in both liquids and gases (collectively called fluids) move randomly. This is called Brownian motion.
    - Robert Brown was the first one observed this in 1827.
    - If a number of particles subject to Brownian motion are present in a given medium and there is no preferred direction for the random oscillations, then over a period of time the particles will tend to be spread evenly throughout the medium.
    - Brownian Motion Examples
        - The motion of pollen grains on still water.
        - Movement of dust motes in a room (although largely affected by air currents)

2. Fluctuation dissipation theorem:-
    - The fluctuation-dissipation theorem which states that the linear response of a given system to an external perturbation is expressed in terms of fluctuation properties of the system in thermal equilibrium.
    - This theorem may be represented by a stochastic equation describing the fluctuation, which is a generalization of the familiar Langevin equation in the classical theory of Brownian motion.

3. Light gas:-
    - The gases which have less mass are known as light gas.
    - For example: Hydrogen, helium.

4. Light according to plank:-
    - Planck postulated that the energy of light is proportional to the frequency, and the constant that relates them is known as Planck's constant (h).
    - His work led to Albert Einstein determining that light exists in discrete quanta of energy, or photons.
    - Light is a vibration of electromagnetic waves.

5. Ensembles:-
	- Ensemble is the idealization of a group of large number of microscopically ,independent systems.In such huge systems,some macroscopic quantities like pressure,volume is same for all the constituent systems.
	- Here the system and surroundings can have partical exchange or energy exchange.