Fundamentals of Physics 8/e 28 - Magnetic Force 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 28-1 What Is Physics? 28-2 What Produces a Magnetic Field? 28-3 The Definition of 28-4 Crossed Fields: Discovery of the Electron 28-5 Crossed Fields: The Hall Effect 28-6 A Circulating Charged Particle 28-7 Cyclotrons and Synchrotrons 28-8 Magnetic Force on a Current-Carrying Wire 28-9 Torque on a Current Loop 28-10 The Magnetic Dipole Moment 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 28-1 What Is Physics? As we have discussed, one major goal of physics is the study of how an electric field can produce an electric force on a charged object. A closely related goal is the study of how a magnetic field can produce a magnetic force on a (moving) charged particle or on a magnetic object such as a magnet. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

28-2 What Produces a Magnetic Field? One way is to use moving electrically charged particles, such as a current in a wire, to make an electromagnet. The other way to produce a magnetic field is by means of elementary particles such as electrons because these particles have an intrinsic magnetic field around them. 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 28-3 The Definition of 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 28-3 The Definition of Vector product 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 28-3 The Definition of Magnetic Field Lines At any point P the magnetic field vector is tangent to the magnetic field lines. The magnitude of the magnetic field vector is proportional to the density of the magnetic field lines. P magnetic field line magnetic field lines P Q 彰化師大教學卓越－普物教材－理學院長郭艷光主持

28-4 Crossed Fields: Discovery of the Electron Cathode Anode J.J. Thomson in 1897 used a version of this tube to investigate the nature of the particle beam that caused the fluorescent spot. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

28-5 Crossed Fields: The Hall Effect 彰化師大教學卓越－普物教材－理學院長郭艷光主持

28-6 A Circulating Charged Particle . electron C r 彰化師大教學卓越－普物教材－理學院長郭艷光主持

28-6 A Circulating Charged Particle 彰化師大教學卓越－普物教材－理學院長郭艷光主持

28-7 Cyclotrons and Synchrotrons The key to the operation of the cyclotron is that the frequency f at which the proton circulates in the magnetic field (and that does not depend on its speed) must be equal to the fixed frequency fosc of the electrical oscillator, or f= fosc (resonance condition). At proton energies above 50 MeV, the conventional cyclotron begins to fail because one of the assumptions of its design—that the frequency of revolution of a charged particle circulating in a magnetic field is independent of the particle’s speed—is true only for speeds that are much less than the speed of light. 彰化師大教學卓越－普物教材－理學院長郭艷光主持

28-8 Magnetic Force on a Current-Carrying Wire . i 彰化師大教學卓越－普物教材－理學院長郭艷光主持

28-9 Torque on a Current Loop 彰化師大教學卓越－普物教材－理學院長郭艷光主持

28-10 The Magnetic Dipole Moment 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 28! 彰化師大教學卓越－普物教材－理學院長郭艷光主持