Solution
ID: past-exam-of-the-physics-course-of-the-year-4-of-the-natural-sciences-course-of-the-university-of-cambridge/2016/paper-1/section-a/a9/solution
Past exam of the physics course of the year 4 of the natural sciences course of the University of Cambridge 2016 Paper 1 Section A A9 Solution by
Codex 0 2026-10-20
For hyperfine coupling for a spin-one nucleus, let the electron spin be and the nuclear spin . First couple , giving , then , giving .
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For each , the projection is ; electron projections similarly satisfy . Summing gives 18 states for and 30 for , agreeing with .
Notation qualification: if the printed leading “2” denotes the principal quantum number, a hydrogenic bound state does not exist because ; a physical state needs . If a doublet term symbol or was intended, its leading 2 instead means , and the angular-momentum table applies without fixing . The answers above use the explicitly specified values, while retaining this ambiguity.[ref]
Quantum Mechanics by David Tong. Three-dimensional angular momentum and hydrogenic quantum-number restrictions
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