In some places I saw that the module of the kinetic orbital momentum of an electron in an atom is a) L^2=l(l+1)h^/(4pi^2) ==> L =h/(2pi)sqrt(l*(l+1)) l=0,1,2,....n-1 b) L=n*h/(2pi) n beeing the energy level of an electron . Now , my opinion is that the first is true . But I saw some problems solved using only the second value . I'm really confused . Which one is it ? Thank you !