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This physics course covers the principles of quantum mechanics, focusing on spin and angular momentum in elementary particles. Topics include spin types, representation of angular momentum, Clebsch-Gordan coefficients, and the relationship between spin and magnetic field. Homework assignments and practice tests are provided.
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Physics 451 Quantum mechanics I Fall 2012 Nov 16, 2012 Karine Chesnel
Quantum mechanics Announcements • Homework this week: • HW #20 Thursday Nov 17 by 10pm • Pb 4.27, 4.28, 4.29, 4.33, 4.34, 4.35 Practice Test 3 review Mon Nov 19 – Tu Nov 20 Test 3 : Monday Nov 26 – Friday Nov 30
orbital spin Quantum mechanics The Spin Types of angular momentum
Representation of Quantum mechanics Agular moment in the atom • Orbital moment (l) • Spin moment (s)
Fermions: (S half-integer) S=1/2 Leptons: electrons,… Quarks: u,b,c,s,t,b • Bosons: (S integer) Photon S=1 Quantum mechanics Spin in elementary particles Each elementary particle is characterized by an immutable spin S Proton, neutron Mesons
Quantum mechanics The spin
Quantum mechanics The spin
Spin up Spin down Quantum mechanics The spin 1/2 The “spinor”
Quantum mechanics Pauli matrices Pb 4.29
Normalization Expectation values etc… Quantum mechanics State of the electron Pb 4.27, 4.28, 4.29
A. 0 • B. • D. • E. Quantum mechanics Quiz 29a When measuring Sx on an electron, what are the possible results?
Possibilities for two spins 1/2 Quantum mechanics Adding spins
Triplet Singlet Quantum mechanics Adding spins 1/2 possibilities
Triplet Singulet Quantum mechanics Adding spins 1/2 Magnitude of the spin momentum ?
Possible values for S: Clebsch- Gordan coefficients Quantum mechanics Adding spins S Pb 4.34, 4.35
Quantum mechanics Clebsch- Gordan coefficients
A. • B. • D. • E. Quantum mechanics Quiz 29b What is the value of the Clebsch-Gordan coefficient ?
S Quantum mechanics The spin and magnetic field
S B Quantum mechanics The spin and magnetic field
z a y x Larmor frequency Quantum mechanics Larmor precession B S Pb 4.32
S Quantum mechanics Stern-Gerlach experiment z B Moves down Moves up