Fundamentals of Physics 8/e 28 - Magnetic Force

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1 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

2 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

3 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

4 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

5 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

6 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

7 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

8 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

9 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

10 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

11 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

12 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

13 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

14 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

15 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

16 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