Phy107Lect28 - HW posted on web page- HW10: Chap 14 Concept...

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Fri. Nov 12 Phy107 Lecture 28 From Last Time… • ‘Philosophical’ effects in quantum mechanics • Interpretation of the wave function: – Calculation using the basic premises of quantum mechanics give highly accurate results… – …but what does it mean? • Superposition of quantum states • Entanglement, action at a distance • Copenhagen interpretation – ‘collapse of the wavefunction’ HW posted on web page— HW10: Chap 14 Concept 8,20,24,26 Prob. 4,8
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Fri. Nov 12 Phy107 Lecture 28 Atoms, Molecules and Solids • Some very basic considerations in quantum mechanics explain some basic properties of atoms, molecules, and solids. • Electron spin: a new quantum effect • Indistinguishability: electrons are identical • Symmetry: qualitative considerations
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Fri. Nov 12 Phy107 Lecture 28 Additional electron properties • Free electron, by itself in space, not only has a charge, but also acts like a bar magnet with a N and S pole. • Since electron has charge, could explain this if the electron is spinning. • Then resulting current loops would produce magnetic field just like a bar magnet. • But… Electron in NOT spinning. As far as we know, electron is a point particle. N S
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Fri. Nov 12 Phy107 Lecture 28 Electron magnetic moment • Why does it have a magnetic moment? • It is a property of the electron in the same way that charge is a property. • But there are some differences – Magnetic moment has a size and a direction – It’s size is intrinsic to the electron, but the direction is variable. • The ‘bar magnet’ can point in different directions.
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Fri. Nov 12 Phy107 Lecture 28 Quantization of the direction • But like everything in quantum mechanics, this direction is quantized. • And also like other things in quantum mechanics, if magnetic moment is very large, the direction quantization is not noticeable. • But for an electron, the moment is very small. – The quantization is a large effect. – In fact, there are only two possible directions. – We call these spin up and spin down.
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Fri. Nov 12 Phy107 Lecture 28 Electron spin orientations • Spin up N S • Spin down
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Fri. Nov 12 Phy107 Lecture 28 Another quantum number • There is a quantum # associated with this property of the electron. • Even though the electron is not spinning, the magnitude of this property is the spin. • The quantum numbers for the two states are +1/2 for the up-spin state -1/2 for the down-spin state • The proton is also a spin 1/2 particle.
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This note was uploaded on 01/05/2012 for the course PHYS 107 taught by Professor N/a during the Spring '08 term at University of Wisconsin.

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Phy107Lect28 - HW posted on web page- HW10: Chap 14 Concept...

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