D. Halliday, R. Resnick, and J. Walker Fundamentals of Physics 8/e 32 - Maxwell's Equations, Models of Magnetism D. Halliday, R. Resnick, and J. Walker 國立彰化師大教學卓越計畫 理學院普通物理整合型教材 主持人：郭艷光院長

彰化師大教學卓越－普物教材－理學院長郭艷光主持 Outline 32-1 What Is Physics? 32-2 Gauss’ Law for Magnetic Fields 32-3 Induced Magnetic Fields 32-4 Displacement Current 32-5 Maxwell’s Equations 32-6 Magnets 32-7 Magnetism and Electrons 32-8 Magnetic Materials 32-9 Diamagnetism 32-10 Paramagnetism 32-11 Ferromagnetism 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 32-1 What Is Physics? This chapter reveals some of the breadth of physics because it ranges from the basic science of electric and magnetic fields to the applied science and engineering of magnetic materials. We conclude our basic discussion of electric and magnetic fields, finding that most of the physics principles can be summarized in only four equations, known as Maxwell’s equations. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

32-2 Gauss’ Law for Magnetic Fields The simplest magnetic structure that can exist is a magnetic dipole. Magnetic monopoles do not exists as far as we know. Instead new pole faces appear on the newly cut faces of the pieces and the net result is that we end up with three smaller magnets, each of which is a magnetic dipole. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

32-2 Gauss’ Law for Magnetic Fields Magnetic Flux For each element we calculate the magnetic flux through it: ΔФi=Bi dAi cosψi => ΣФi=ΣBi dAi cosψi SI magnetic flux unit: T‧m² known as the “Weber” (Wb) For any closed surface:ФB=0 彰化師大教學卓越－普物教材－理學院長郭艷光主持

32-3 Induced Magnetic Fields Maxwell’s law of induction : 彰化師大教學卓越－普物教材－理學院長郭艷光主持

32-4 Displacement Current 彰化師大教學卓越－普物教材－理學院長郭艷光主持

32-4 Displacement Current 彰化師大教學卓越－普物教材－理學院長郭艷光主持

32-4 Displacement Current B O 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 32-5 Maxwell’s Equations 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 32-6 Magnets N S Fig.b : Side view horizontal Compass needle N S Fig.a : Top view Geographic North Compass needle The magnetism of earth: Earth has a magnetic field that can be approximated as the field of a very large bar magnet that straddles the center of the planet. The dipole axis does not coincide exactly with the rotation axis but the two axed form an angle of 11.5˚. The direction of the earth’s magnetic field at any location is described by two angles: Field declination θ is defined as the angle between the geographic north and the horizontal component of the earth’s magnetic field. Field inclination ψ is defined as the angle between the horizontal and the earth’s magnetic field. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

32-7 Magnetism and Electrons Orbital magnetic dipole moment. Spin magnetic dipole moment:In addition to the orbital angular momentum an electron has what is known as “intrinsic” or “spin” angular momentum. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

32-7 Magnetism and Electrons 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 32-8 Magnetic Materials Materials can be classified on the basis of their magnetic properties into three categories: Diamagnetic, paramagnetic, and ferromagnetic. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 32-9 Diamagnetism . C e 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 32-9 Diamagnetism . C e 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 32-10 Paramagnetism When the ratio B/T is below 0.5 the magnetization M of a paramagnetic material follows Curie’s law: The atoms of paramagnetic materials have a net magnetic dipole moment in the absence of an external magnetic field.This moment is the vector sum of the electron magnetic moments. For very high magnetic fields and/or low temperatures, all magnetic moments are parallel to B field and the magnetization. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 32-11 Ferromagnetism Ferromagnetism is exhibited by Iron, Nickel, Cobalt, Gadolinium, Dysprosium and their alloys. Hysteresis Magnetic domains 彰化師大教學卓越－普物教材－理學院長郭艷光主持

彰化師大教學卓越－普物教材－理學院長郭艷光主持 End of chapter 32! 彰化師大教學卓越－普物教材－理學院長郭艷光主持