《Fundamentals of Physics精品教学-华南理工》28 Magnetic Fields.pptVIP

Electromagnetism Electrical phenomena → Electricity Magnetic phenomena → Magnetism Electricity produces magnetism Magnetism produces electricity Electricity and magnetism are connected each other → Electromagnetism (1820) This connection is represented in the Maxwell’s law Fundamentals of Physics 21 Electric Charge Fundamentals of Physics 28 Magnetic Fields 28-2 What Produces a Magnetic Field? Two methods to produce magnetic field (1) Electromagnet moving charge, current. (2) permanent magnet intrinsic field. Magnetic field: magnetic monopole does not exist. Electric field: produce and detect. Fundamentals of Physics 28 Magnetic Fields 28-3 The Definition of Magnetic Field The definition of electric field (charge at rest) The definition of magnetic field (charge in motion) Fundamentals of Physics 28 Magnetic Fields F is always perpendicular to v and B, cannot change the particle’s speed. 28-3 The Definition of Magnetic Field Magnetic Field Lines: direction and magnitude Form closed loops North pole; south pole Interaction between poles Fundamentals of Physics 28 Magnetic Fields Earth’s magnetic field 28-3 The Definition of Magnetic Field Fundamentals of Physics 28 Magnetic Fields Animal migrations 28-3 The Definition of Magnetic Field Earths aurora A magnetic field B=1.2 mT, is directed horizontally outward. A proton with kinetic energy 5.3 MeV enters the region, moving vertically upward. What is the force acting on the proton? (mP=1.67×10-27 kg) Fundamentals of Physics Sample Problem 28-4 Crossed Fields: Discovery of the Electron E B Fundamentals of Physics 28 Magnetic Fields 28-4 Crossed Fields: Discovery of the Electron Fundamentals of Physics 28 Magnetic Fields E B Thomson claimed that these particles are found in all matter; and they are lighter than the lightest atom (H) by a factor of more than 1000. L y =0 28-5 Crossed Fields: The Hall Effect Fundamentals of Physics 28 Magnetic Fields charge sign; charge densi