Hello, This was part of my midterm exam that i couldn't solve. Any help is extremely appreciated. Problem: The K.E. of a rotating top is given as L^2/2I where L is its angular momentum and I is its moment of inertia. Consider a charged top placed at a constant magnetic field. Assume that the magnetic momentum of the top is proportional to L, M=KL (K is a cst that can be derived from the classical distribution of the charge that is known). Write the Hamiltonian for the quantum top and find the energy eigenstates and energy eigenvalues of the quantum top. This is what i wrote during the exam: T= L^2/2I and V= -M.B (where B is the magnetic field) so H=L^2/2I -M.B = L^2/2I - KL.B then i said since it's a rotating top let's suppose that B is along the z-axis which limits our L to L_z then, H= L_z( L_z/2I - K.B_z) and i stopped there. Now looking calmly at the problem, i realized that i absolutely looked over the fact that it is charged. I think i need to be using A ( the electrostatic potential) along with B but still i have no idea how to start... Please any help would be awesome! Thank you.