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Explain, using electromagnetic analogy or otherwise, how one can understand the origin of the magnetic moment of an atomic state in terms of its constituent elec- trons and their angular momenta. [3] Explain how the magnetic moment of an atomic state can give rise to the "spatial quantisation" of the state in the presence of a uniform applied magnetic field. [5] Explain how spatial quantisation accounts for the Zeeman splitting of atomic line spectra by considering how a magnetic field modifies the energy levels of an atom. What quantum number is needed to classify the split energy levels? [4]