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### Course: Class 11 Physics (India)>Unit 17

Lesson 2: Kinetic molecular theory of gases

# Boltzmann's constant

Explore Ludwig Boltzmann's groundbreaking atomic theory and his constant's role in thermal physics. Understand the kinetic-molecular explanation of temperature, the ideal gas law, and the concept of entropy. Uncover the microscopic details of gas molecules and their impact on our understanding of heat energy. Created by David SantoPietro.

## Want to join the conversation?

• What if the pressure is in atmospheric pressure units or _mm of Hg column, what is the gas constant then??
• If u use atm as pressure unit,
R=0.0821 L atm K^−1 mol^−1
If u use mm of Hg,
R=62.33 L mmHg K^-1 mol^-1
• If heat is really just Kinetic Energy of gas molecules as he says at , then how can heat be transferred through a vacuum like in space?
• Heat is not just Kinetic Energy. IMHO, I'd rather think of Heat as a form of energy, than thinking of is as a measure of how-much-things-vibrate .

Digging the physics behind, phonon is the best way to describe heat. :)

Heat can be transferred is one of three forms. Namely Conduction (solid-to-solid), Convection(liquid-to-liquid) or Radiation(thru vacuum). The first two are quite straightforward, but vacuum.. is a bit different(or shall I say.. special?).

I would like to use a light bulb as example. To turn on tungsten light bulb :
[1] Turn on the circuit
[2] Bulb will light up
[3] After a while the bulb surface and air at its surrounding gets hot.

In step [1], the Energy conversion is : Chemical Energy > Electrical Energy.
In [2], Electrical Energy > Heat Energy > Light Energy
In [3], Light Energy > Heat Energy(on bulb surface and on its surrounding).

In [2], the tungsten filament gets hot, then it radiates. it "radiates", means that the emitted light is within the human visibility spectrum (wavelength 390-700 nm).
At the same time, the tungsten doesn't (or very minimally) conduct heat via conduction or convection as the medium is vacuum. The heat was radiated as heat energy packets, in literature, referred as phonon.

In [3], every energy packets are absorbed by other material with mass and translated into vibration(or kinetic energy). :)

Heat is an interesting physical properties. Its application includes solar energy harvester and the natures photosynthesis (the only way for earth to get Sun's energy).

p/s : I had exactly the same question years back. I'd say that.. the real physics behind it no way straightforward, at least for me. Happy exploring. \(^_^)/
• Can we technically say that the Boltzmann constant is in SI base units of J/K*molecules? I assume that part was left out because in the microscopic ideal gas law we multiply it by N (number of molecules).
• Boltzman constant stand for gas, constant for single molecule?
as the unit of Boltzman constant is j/Molecule-Kelvn ?
• just wanted to point out that the container at is an optical illusion. Depending on your perspective, it looks cube, but there are two possible "orientations" of the cube. Neat!
(1 vote)
• Why, when the Quantum Boltzmann distribution function is deduced from the canonical distribution, this canonical distribution can be applied to just one molecule, since, as we know, the physical physics studies the macrocoscopic bodies (with a very large number of atoms / molecules)?
(1 vote)
• i hv a doubt regarding boyles law.
boyles law holds good for any gas at high temperature and low pressure but it also says this law is independent of the selection of scale of temperature since temperature is kept constant..