# Physical Constants

In Physics there are many constants. These relate the real universe (or the bits we think we understand!) to the human-invented scales of measurement.

Name Value Equation/notes
Atomic mass unit 1 u = 1.661 x 10-27 kg = 931.5 MeV c-2
Avogadro constant NA = 6.02 x 1023 mol-1
Boltzmann constant k = 1.38 x 10-23 J K-1
Coulomb's law constant 1/(4πε0) = 8.99 x 109 N m2 C-2
Electric permittivity ε0 = 8.85 x 10-12 N-1 m-2 C2
Gravitational constant G = \$6.67 x 10^{-11} N⋅(m/{kg})^2\$
Magnetic permeability \$μ_0 = 4π x 10^{-7} T m A^{-1}\$
Electron charge e = 1.60 x 10-19 C
Electron mass me = 9.11 x 10-31 kg = 5.49 x 10-4 u = 0.511 MeV c-2
Neutron mass mn = 1.675 x 10-27 kg = 1.008 665 u = 940 MeV c-2
Proton mass mp = 1.673 x 10-27 kg = 1.007 276 u = 938 MeV c-2
Planck constant h = 6.63 x 10-34 J s
Speed of light (vacuum) c = 3.00 x 108 m s-1
Stefan-Boltzmann constant σ = 5.67 x 10-8 W m-2 K-4
Universal gas constant R = 8.31 J mol-1 K-1

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