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chapter_28 - Chapter 28 M agneti c Fi el d 28.1 What i s...

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Chapter 28. Magnetic Field 28.1. What is Physics? 28.2. What Produces a Magnetic Field? 28.3. The Definition of Magnetic Field 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
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What is Physics? Permanent magnets A magnet has two poles, a north pole and a south pole No Magnetic monopole available in nature.
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The magnetic forces Like poles repel each other, and unlike poles attract.
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The magnetic field A magnetic field exists in the region around a magnet. The magnetic field is a vector that has both magnitude and direction. The direction of the magnetic field at any point in space is the direction indicated by the north pole of a small compass needle placed at that point.
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The magnetic field line The lines originate from the north pole and end on the south pole; they do not start or stop in midspace. The magnetic field at any point is tangent to the magnetic field line at that point. The strength of the field is proportional to the number of lines per unit area that passes through a surface oriented perpendicular to the lines. The magnetic field lines will never come to cross each other.
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What Produces a Magnetic Field? Moving electrically charged particles, such as a current, produce a magnetic field Permanent magnet. Elementary particles such as electrons have an intrinsic magnetic field around them. The magnetic fields of the electrons in certain materials add together to give a net magnetic field around the material. Such addition is the reason why a permanent magnet has a permanent magnetic field. In other materials, the magnetic fields of the electrons cancel out, giving no net magnetic field surrounding the material                                                                                                                                                                
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Magnetic force on a Charged Particle When a charge is placed in a magnetic field, it experiences a magnetic force if two conditions are met: 1. The charge must be moving. No magnetic force acts on a stationary charge. 2. The velocity of the moving charge must have a component that is perpendicular to the direction of the field.
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Magnetic force on a Charged Particle Right-Hand Rule The force acting on a charged particle moving with velocity through a magnetic field is always perpendicular to and .
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Check Your Understanding Two particles, having the same charge but different velocities, are moving in a constant magnetic field (see the drawing, where the velocity vectors are drawn to scale). Which particle, if either, experiences the greater magnetic force? (a) Particle 1 experiences the greater force, because it is moving perpendicular to the magnetic field. (b) Particle 2 experiences the greater force, because it has the
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