Symbol | Represents |

| Planck constant |

$\hslash $ | reduced Planck constant |

| speed of light |

| velocity of the electron |

| atomic number |

${R}_{\infty}$ | Rydberg constant |

${n}_{1}$ | the principal quantum number of an energy level |

${n}_{2}$ | the principal quantum number of an energy level for the atomic electron transition |

${\u03f5}_{0}$ | vacuum permittivity |

$\alpha $ | Fine structure constant |

| elementary charge |

$\lambda $ | Photon wavelength |

${\lambda}_{e}$ | Compton wavelength electron |

${\overline{\lambda}}_{e}$ | Reduced Compton wavelength electron |

${m}_{e}$ | rest mass of electron |

${m}_{P}$ | rest mass of proton |

| momentum |

| energy |

${E}_{k}$ | kinetic energy |