1. The problem statement, all variables and given/known data A magnetic resonancy experiment is realized using hydrogen atoms in their ground state. A constant magnetic field [itex]B_0[/itex] duplicate the magnetic energy levels in the atoms and an oscillating magnetic field [itex]B_ \omega[/itex] is synchronized to the frequency that corresponds to the transition between these levels. Calculate the value of the frequency of resonance for a field [itex]B_0 =2000G[/itex]. 2. Relevant equations Somes. 3. The attempt at a solution I think I know how to solve the problem if the atoms weren't in their ground state. What makes me doubt about my whole understanding of the quantum numbers and the hydrogen atom is... If n=1, the quantum number l must be worth 0. Since [itex]m_l[/itex] goes from [itex]-l[/itex] to [itex]l[/itex], it must also be worth 0. So how can there be any duplication of lines? Edit: It isn't stated but I guess I must assume that the atoms absorb photons to reach the shell n=2. Is this right?