Consider a hydrogen atom with the electron in the 2p state. the magnetic field at the nucleus produced by the orbiting electron has a value of 12.5 t.
the proton can have its magnetic moment aligned in ei- ther of two directions perpendicular to the plane of the electrons orbit.
because of the interaction of the protons magnetic moment with the electrons mag- netic field, there will be a difference in energy be- tween the states with the two different orientations of the protons magnetic moment.

find that energy dif- ference in electron volts.