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Boltzmann constant

The Boltzmann constant relates the average kinetic energy of particles to temperature: E ≈ k_B·T. Since 2019 it is an exact defining constant of the SI, and its fixed value defines the kelvin. It also connects entropy to the number of microstates through S = k_B ln W, bridging the microscopic and macroscopic views of thermodynamics.

Used in

  • Statistical thermodynamics
  • Kinetic theory of gases

Source: SI Brochure 9th ed. — exact defining constant