where is the Rydberg constant ( typically between 1 eV and 103 eV ) , Z is the charge of the atom 's nucleus , is the principal quantum number , e is the charge of the electron , is Planck 's constant , and c is the speed of light . ( typically between 1 eV and 103 eV ) , where is the Rydberg constant , Z is the Atomic number , n is the principal quantum number , is Planck 's constant , and c is the speed of light .