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Ch. 32 Magnetic of Matter (Maxwell Eqns.)

Ch. 32 Magnetic of Matter (Maxwell Eqns.). § 32-1 : Magnets. No magnetic dipole! (N 극이나 S 극만 갖는 자석은 없다 . ). Electric dipole exists! (+,- charge 만 따로 분리가능 ). § 32-2 Gauss’ Law. § 32-3 The magnet of Earth. 왜 지구는 자기장을 갖는가 --> dynamo. Note) 지구의 자기 북극 , 남극이 고정되 있지 않다.

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Ch. 32 Magnetic of Matter (Maxwell Eqns.)

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  1. Ch. 32 Magnetic of Matter (Maxwell Eqns.) § 32-1 : Magnets No magnetic dipole! (N극이나 S극만 갖는 자석은 없다. ) Electric dipole exists! (+,- charge만 따로 분리가능) § 32-2 Gauss’ Law § 32-3 The magnet of Earth • 왜 지구는 자기장을 갖는가 • --> dynamo • Note) 지구의 자기 북극, • 남극이 고정되 있지 않다.

  2. § 32-4 Three ways to generate B from e- 1) drift : B e- v 2) spin : pure quantum mechanical property of e- 3) orbiting : § 32-5 Three types of magnetic materials • paramagnetism : (상자성체) Binduced//Bex • : Al,Ti,Mg,Na • diamagnetism : (반자성체) antiparallel • : Cu,Ag,Au,Bi Binduced Bex • ferromagnetism : (강자성체) strong alignment • : Fe,Co,Ni : Transition Metal Note)

  3. Para & dia : linear magnetic material • B=H ( : constant) B H B • ferro : nonlinear • B=(H)H H Note) B=H=0H+0M D=H= 0H+P § 32-8 Ferro Magnetism (Permanent Magnet Fe3O4) NeoMax (Nd2Fe14B) Cormax (Co,Sn,Fe,O) Alnico Mk-steal Ferrite Area가 클수록 Ferromagnetic Property가 좋다. • Hysteresis Ferromagnetic materials B Linear material H Trace area:0

  4. Note) Ferromagnetic Material 은 magnetic domain들로 이루어져 있다. 외부 에서 어떤 자극도 없는 평상시 에는 domain들이 randomly oriented되있기 때문에 Btotal이 0이다. 그러나 외부에서 H가 걸리면 domain들이 정렬하여 Btotal이 0이 아니게 되게 된다. 이때 외부 H를 제거하여도 domain들이 완 전히 random orientation되지 않기 때문에 B가 존재하게 된다. ==>Hysteresis curve가 나타남. H가 가해지면 H가 제거된후 Initial B0 Btot = 0 H M Note) 옆 그림과 같이 Ferro 에 열을 가하면 magnetization 이 줄어들어 TTc가 되면 Para가 된다. * ferrofluid (Magnetic fluid) Ferro Para T/Tc 1.0 Tc : Curie Temperature : 1000K(Fe) § 32-9 Induced Magnetic fields id : displacement current

  5. By Stoke’s Theorem. § 32-11 Maxwell’s Equations

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