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Physical Constants

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    Name Symbol Value Unit
    Number \(\pi\) \(\pi\) 3.14159265358979323846  
    Number e e 2.71828182845904523536  
    Euler’s constant   0.577215664901532860606  
    Elementary charge \(e\) \(1.60217733\cdot10^{-19}\)


    Gravitational constant \(G,\kappa\) \(6.67259\cdot10^{-11}\) m\(^3\)kg\(^{-1}\)s\(^{-2}\)
    Fine-structure constant \(\alpha=e^2/2hc\varepsilon_0\) \(\approx1/137\)  
    Speed of light in vacuum \(c\) \(2.99792458\cdot10^8\) m/s (def)
    Permittivity of the vacuum \(\varepsilon_0\) \(8.854187\cdot10^{-12}\) F/m
    Permeability of the vacuum \(\mu_0\) \(4\pi\cdot10^{-7}\) H/m
    \((4\pi\varepsilon_0)^{-1}\)   \(8.9876\cdot10^9\) Nm\(^2\)C\(^{-2}\)
    Planck’s constant \(h\) \(6.6260755\cdot10^{-34}\)


    Dirac’s constant \(\hbar=h/2\pi\) \(1.0545727\cdot10^{-34}\) Js
    Bohr magneton \(\mu_{\rm B}=e\hbar/2m_{\rm e}\) \(9.2741\cdot10^{-24}\) Am\(^2\)
    Bohr radius \(a_0\) \(0.52918\) Å
    Rydberg’s constant \(Ry\) 13.595 eV
    Electron Compton wavelength \(\lambda_{\rm Ce}=h/m_{\rm e}c\) \(2.2463\cdot10^{-12}\) m
    Proton Compton wavelength \(\lambda_{\rm Cp}=h/m_{\rm p}c\) \(1.3214\cdot10^{-15}\) m
    Reduced mass of the H-atom \(\mu_{\rm H}\) \(9.1045755\cdot10^{-31}\) kg
    Stefan-Boltzmann’s constant \(\sigma\) \(5.67032\cdot10^{-8}\)


    Wien’s constant \(k_{\rm W}\) \(2.8978\cdot10^{-3}\) mK
    Molar gasconstant \(R\) 8.31441 J\(\cdot\)mol\(^{-1}\cdot\)K\(^{-1}\)
    Avogadro’s constant \(N_{\rm A}\) \(6.0221367\cdot10^{23}\) mol\(^{-1}\)
    Boltzmann’s constant \(k=R/N_{\rm A}\) \(1.380658\cdot10^{-23}\) J/K
    Electron mass \(m_{\rm e}\) \(9.1093897\cdot10^{-31}\)


    Proton mass \(m_{\rm p}\) \(1.6726231\cdot10^{-27}\) kg
    Neutron mass \(m_{\rm n}\) \(1.674954\cdot10^{-27}\) kg
    Elementary mass unit \(m_{\rm u}=\frac{1}{12}m(^{12}_{~6}\)C) \(1.6605656\cdot10^{-27}\) kg
    Nuclear magneton \(\mu_{\rm N}\) \(5.0508\cdot10^{-27}\) J/T
    Diameter of the Sun \(D_\odot\) \(1392\cdot10^6\)


    Mass of the Sun \(M_\odot\) \(1.989\cdot10^{30}\) kg
    Rotational period of the Sun \(T_\odot\) 25.38 days
    Radius of Earth \(R_{\rm A}\) \(6.378\cdot10^6\) m
    Mass of Earth \(M_{\rm A}\) \(5.976\cdot10^{24}\) kg
    Rotational period of Earth \(T_{\rm A}\) 23.96 hours
    Earth orbital period Tropical year 365.24219879 days
    Astronomical unit AU \(1.4959787066\cdot10^{11}\) m
    Light year lj \(9.4605\cdot10^{15}\) m
    Parsec pc \(3.0857\cdot10^{16}\) m
    Hubble constant \(H\) \(\approx(75\pm25)\) km\(\cdot\)s\(^{-1}\cdot\)Mpc\(^{-1}\)

    Physical Constants is shared under a CC BY license and was authored, remixed, and/or curated by Johan Wevers.

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