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Download Ch33 The Magnetic Field
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講者: 許永昌 老師 1 Contents (起)Discovering magnetism Compass needle : a probe of Magnetic field (承)Moving charge is the source of magnetic field (轉)The magnetic force on a moving charge current-carrying wires. Force and Torque on Current loops (合)Microscopic discussion of Magnetic properties of matter. 2 (起)Discovering magnetism (請預讀 P998~P1000) 1. Definition 2. Interaction 3. No magnetic monopole 4. Differ from electricity 3 Compass needle : a probe of (請預讀P1000~P1002) Oersted’s discovery: In the midst of a 1819. in You should know and be used to these notations. 4 (承)Moving charge is the source of magnetic field (請預讀P1000~P1011) Biot-Savart Law (1875): Permeability constant: m0=4p10-7 Tm/A SI Unit of magnetic field: T (tesla) 5 Moving charges Current (請預讀 P1005~P1006) 2 1 v Ds Dt Dt: the time period used for a charge carrier moved from surface 1 to 2. Dq: The net charge inside the segment. =the net charge pass through surface 2 during Dt. m0 I Ds rˆ 2 4p r Dq I Dt 6 Current Loop (請預讀P1007~P1012) A current loop is as a magnetic dipole. 7 Ampere’s Law & Solenoid (請預讀 P1012~P1017) Ampere’s Law: Example: B dr m I 0 through Solenoid: BL m0 NI B m0 nI . 8 (轉)The magnetic force on a moving charge (請預讀P1018~P1026) Lorentz force: Fon q qE qv B. We get FB on wire I l B. 9 Force and Torque on Current loops(請預讀P1026~P1028) 4 Fi 0, i 1 will be independent of the choice of origin. IA B m B. m : magnetic dipole moment = IA. 10 (合)Microscopic discussion of Magnetic properties of matter (請預讀 P1028~P1031) Candidates: Electron orbits They will tend to cancel each other. Electron has Mass: interact with FG. Charge: interact with E. : interact with B. Ferromagnetic material: The spins are aligned to be organized into magnetic domain. 11