E物质的磁性.pptVIP

* Chapter 10 Magnetism of matter §1 Magnetic medium and its classification §2 Magnetization Magnetic field intensity §3 Ferromagnetic substance §4 Example §1 Magnetic medium and its classification 1 Magnetic medium Magnetic medium 磁介质 在磁场作用下发生变化，并能反过来影响磁场的物质 (2) The Magnetization of magnetic medium :磁介质的磁化 磁介质在磁场作用下的变化称为磁化 2 The classification of magnetic medium Relative permeability 相对磁导率 In medium: 各种物质都具有一定的磁性，都能对磁场产生影响，因此一切物质都可以认为是磁介质。 (2) Paramagnetic medium 顺磁质 manganese、chrome、oxygen etc. The B in medium is larger than in vacuum. (3) Ferromagnetic medium 铁磁质 iron、cobalt、nickel etc. The B in medium is more lareger than in vacuum. Diamagnetic medium 抗磁质 copper、plumbum、hydrogen etc. The B in medium is less than in vacuum. Typically ?r differs from unity by only a few parts in 105 §2 Magnetization 磁化强度 Magnetic field intensity 磁场强度 1 The Magnetization of magnetic medium The motion of electron spin: 电子自旋运动： spin magnetic moment自旋磁矩 ； The motion of electron orbit:电子绕核运动： orbit magnetic moment 轨道磁矩； Molecular magnetic moment 分子磁矩,固有磁矩： 所有电子的轨道磁矩和自旋磁矩的矢量和。 Molecular current：分子电流 分子磁矩用等效的圆电流表示。 (1) Molecular magnetic moment 分子磁矩 (2) Additional magnetic moment 附加磁矩 In an external magnetic induction, the every electron of molecule experiences force which is called Lorentz force. 电子的运动状态发生改变。这时，每个电子的运动，除了自旋运动和绕核运动之外，还要附加一个以外磁场为轴线的转动，称为电子的进动— the precessional motion of electron. 无外磁场时，分子磁矩的排列杂乱无章； In an external magnetic induction, molecular magnetic moment experiences torques It shows that the magnetic moment tends to orient itself parallel to the field 分子磁矩沿外磁场方向排列------顺磁性 paramagnetism 其方向总是与外磁场相反—抗磁性 diamagnetism ? 用电磁感应现象可以说明附加磁矩方向与外磁场方向相反： If the flux through a circuit changes, an electromotive force is induced around it. The polarity of the induced emf is such as to oppose the change that caused it. The induced current always flows to create a magnetic field that opposite the change in flux through the circui