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Finish EM Ch.5: Magnetostatics Methods of Math. Physics, Thus. 10 March 2011, E.J. Zita Lorentz Force Ampere’s Law Maxwell’s equations (d/dt=0) Preview: Full Maxwell Equations (d/dt≠0) Magnetic vector potential A || Electrostatic potential V BC Multipole expansion
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Lorentz Force p.220 #10 (a)
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Lorentz Force p.220 #12
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Ampere’s Law p.231 #13-16 You choose…
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Ampere’s Law p.231 #14
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Ampere’s Law p.231 #15
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Ampere’s Law p.231 #16
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Four laws of electromagnetism
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Electrodynamics Changing E(t) make B(x) Changing B(t) make E(x) Wave equations for E and B Electromagnetic waves Motors and generators Dynamic Sun
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Full Maxwell’s equations
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Maxwell’s Eqns with magnetic monopole Lorentz Force: Continuity equation:
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Vector Fields: Helmholtz Theorem For some vector field F, if the divergence = D = F, and the curl = C = F then (a) what do you know about C ? and (b) Can you find F? (a) C = 0, because ( F) 0 (b) We can find F iff we have boundary conditions, and require the field to vanish at infinity. Helmholtz: A vector field is uniquely determined by its div and curl (with BC)
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Vector Fields: Potentials.1 For some vector field F = - V, find F : (hint: look at identities inside front cover) F = 0 → F = - V Curl-free fields can be written as the gradient of a scalar potential (physically, these are conservative fields, e.g. gravity or electrostatic).
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Theorem 1 – examples The second part of each question illustrates Theorem 2, which follows…
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Vector Fields: Potentials.2 For some vector field F = A, find F : F = 0 → F = A Divergence-free fields can be written as the curl of a vector potential (physically, these have closed field lines, e.g. magnetic).
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Optional – Proof of Thm.2
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Practice with vector field theorems
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Magnetic vector potential
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Electrostatic scalar potential V
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Electric dipole expansion of an arbitrary charge distribution (r) (p.148) P n (cos ) are the Legendre Polynomials
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Multipole expansion
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Magnetic field of a dipole B= A, where
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Spring quarter in E&M Dynamics! dE/dt and dB/dt Bohm-Aharanov effect (A >B) Faraday’s law, motors, generators Magnetic monopole: Blas Cabrera’s measurement Conservation laws, EM energy EM waves Relativistic phenomena EM field tensor
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Spring quarter in MMP Tuesday: Boas and DiffEq → Hamiltonians / Lagrangians Thursday: Quantum Mechanics Friday: Electromagnetism and Research
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