In atomic physics, the bound states of an electron in a hydrogen atom show us useful examples of degeneracy. In this case, the Hamiltonian commutes with the total orbital angular momentum L ^ ^ 2 , its component along the z-direction, L ^ ^ z , total spin angular momentum S ^ ^ 2 and its z-component S ^ ^ z . The quantum numbers corresponding to these operators are ℓ ℓ , m ℓ ℓ , s (always 1/2 for an electron) and m s respectively.