# Physics Course/Physics Constants

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Constant Name Definition
Mass of an electron me = 9.1093897 × 10-31 kg
Mass of a proton mp = 1.6726231 × 10-27 kg
Mass of a neutron mn = 1.6749286 × 10-27 kg
Elementary charge e = 1.60217653 × 10−19 C
Unified atomic mass unit 1 u = 1.66056×10−27 kg
Constant in Coulomb's law K = 8.988 × 109 N·m2·kg-2

Constant Name Definition
Permeability of vacuum μ0 = 4π × 10−7T2·m3·J-1 = 12.566370614 × 10−7 T2·m3·J-1
Permittivity of vacuum ε0 = 1/(μ0c2) = 8.854187817 × 10−12 C2·J-1·m-1

Constant Name Definition
Molar gas constant R = 8.314472 J·mol-1·K-1
Molar Volume Vmol = 22.41383 m3·kmol-1
Avogadro constant NA = 6.0221415 × 1023 mol-1

Constant Name Definition
Absolute zero temperature 0 K = −273.15 °C
Speed of light in vacuum c = 2.99792458 × 108 m·s-1
Newtonian constant of gravitation G = 6.6742 × 10−11 m3·kg-1 s-2
Planck constant h = 6.6260693 × 10−34 J·Hz-1 = 4.136 × 10-15 eV·s;
Planck constant over ${\displaystyle 2\pi }$ ${\displaystyle \hbar }$= 1.05457148 × 10−34 J·s
Boltzmann's constant k = 1.3806505 × 10−23 J K-1
Stefan-Boltzmann constant σ = 5.670400 × 10−8 W·m-2·K-4
Bohr radius a0 = 5.292 × 10−11 m
Electron radius re = 2.81792 × 10-15

Fine structure constant α = e2/(2ε0hc) = 1/137.0359895 = 7.2974 × 10-3
Thomson cross-section σe = 6.652 × 10−29 m2

Some values from the 2002 CODATA recommended values of the Fundamental Physical Constants. See Constants Information at NIST.