物理与光电工程学院：《大学物理》课程PPT教学课件（讲稿，英文第三版）Chapter 25 Magnetism

Chapter 25 Magnetism 第十一章稳恒磁场 Chapter 25 Magnetism 1. Magnet and Magnetic Field 2. Definition of Magnetic Field 3. Force on an Electric Charge Moving in a Magnetic Field 4. Torque on a Current Loop

Chapter 25 Magnetism 第十一章 稳恒磁场 Chapter 25 Magnetism 1. Magnet and Magnetic Field 2. Definition of Magnetic Field 3. Force on an Electric Charge Moving in a Magnetic Field 4. Torque on a Current Loop

Chapter 25 Magnetism 第十一章稳恒磁场 New words and Expressions magnetic monopole 磁单极 magnet 磁铁 magnetic phenomena 磁现象 north(south) pole 南(北极 cyclotron frequency 回旋加速器 aurora borealis 极光 mass Spectrometer 质谱仪 Hall effect 霍尔效应 Hall EMF 霍耳电压 magnetic dipole moment 磁矩

Chapter 25 Magnetism 第十一章 稳恒磁场 New words and Expressions magnetic monopole 磁单极 magnet 磁铁 magnetic phenomena 磁现象 north (south) pole 南(北)极 cyclotron frequency 回旋加速器 aurora borealis 极光 mass Spectrometer 质谱仪 Hall effect 霍尔效应 Hall EMF 霍耳电压 magnetic dipole moment 磁矩

Chapter 25 Magnetism 第十一章稳恒磁场 25-1. Magnets and Magnetic Fields (P580-582 I Magnetic phenomena Magnets used in: Compass; refrigerator-door; microphone, computer disk North geographic pole Magnetic Compass pole Magnetic po ole South geographic pole

Chapter 25 Magnetism 第十一章 稳恒磁场 25-1.Magnets and Magnetic Fields (P580-582) Magnets used in: Compass; refrigerator-door; microphone; computer disk; … 1 Magnetic phenomena I

Chapter 25 Magnetism 第十一章稳恒磁场 2 Basic concepts Poles: the magnetic effect is strongest North (South) pole: The pole of a freel suspended magnet that points to geographic north(south). 北极 南极 There are force between poles Unlike poles attract, and unlike poles repel

Chapter 25 Magnetism 第十一章 稳恒磁场 Poles: the magnetic effect is strongest. North (South) pole: The pole of a freely suspended magnet that points to geographic north (south). There are force between poles. Unlike poles attract, and unlike poles repel. 北极 南极 2 Basic Concepts

Chapter 25 Magnetism 第十一章稳恒磁场 N Repulsive N S N Repulsive S N Attractive If you break a magnet in half, you dont obtain isolated north and south poles; instead, two new magnets are produced. No magnetic monopole has been observed

Chapter 25 Magnetism 第十一章 稳恒磁场 If you break a magnet in half, you don’t obtain isolated north and south poles; instead, two new magnets are produced. No magnetic monopole has been observed

Chapter 25 Magnetism 第十一章稳恒磁场 Magnetic field lines: The direction of the magnetic field is tangent to a line at any point, and the number of lines per unit area is proportional to the strength of the magnetic N三三目 field

Chapter 25 Magnetism 第十一章 稳恒磁场 The direction of the magnetic field is tangent to a line at any point, and the number of lines per unit area is proportional to the strength of the magnetic field. Magnetic field lines:

Chapter 25 Magnetism 第十一章稳恒磁场 25-3 Definition of Electric Field(P583-586) 运动电荷←→磁场←→运动电荷 1 Definition of B F=0 带电粒子在磁场中运 动所受的力与运动方向有 关 实验发现带电粒子在 磁场中沿某一特定直线方 向运动时不受力,此直线 方向与电荷无关

Chapter 25 Magnetism 第十一章 稳恒磁场 25-3. Definition of Electric Field (P583-586) x y z o 运动电荷 磁场 运动电荷 F = 0  1 Definition of B  + v  带电粒子在磁场中运 动所受的力与运动方向有 关. 实验发现带电粒子在 磁场中沿某一特定直线方 向运动时不受力，此直线 方向与电荷无关. v +  v  v 

Chapter 25 Magnetism 第十一章稳恒磁场 带电粒子在磁场中沿 其他方向运动时F垂直 于⑦与特定直线所组成 的平面 当带电粒子在磁场中 垂直于此特定直线运动时 受力最大 正电荷负电荷■ max max CC 磁感强度B的定义:当 正电荷垂直于特定直线运动 mc大小与q,C无关时,受力Fm将m×方 向定义为该点的B的方向

Chapter 25 Magnetism 第十一章 稳恒磁场 带电粒子在磁场中沿 其他方向运动时 垂直 于 与特定直线所组成 的平面. F  v  当带电粒子在磁场中 垂直于此特定直线运动时 受力最大. ⊥ F = F = F    max qv Fmax 大小与 q,v 无关 磁感强度 的定义：当 正电荷垂直于 特定直线运动 时，受力 将 方 向定义为该点的 B的方向.  Fmax  v   Fmax  B  Fmax  qv

Chapter 25 Magnetism 第十一章稳恒磁场 磁感强度B的定义:当 max 正电荷垂直于特定直线运动 时,受力P将F×7方 x向定义为该点的B的方向 磁感强度大小A、下mx magnitude max 运动电荷在磁场中受力 B g0×B Lorentz’ s Force

Chapter 25 Magnetism 第十一章 稳恒磁场 q + v  B  Fmax  磁感强度 的定义：当 正电荷垂直于特定直线运动 时，受力 将 方 向定义为该点的 B 的方向.  Fmax  v   Fmax  B  qv F B max 磁感强度大小 = magnitude 运动电荷在磁场中受力 F q B    = v —— Lorentz’s Force

Chapter 25 Magnetism 第十一章稳恒磁场 2 Unit of Magnetic Field 单位特斯拉I(T=NAm SI unit: Tesla(T), Gauss or N/(Am) IT=10G(gauss) 地磁场B earth 5×105T

Chapter 25 Magnetism 第十一章 稳恒磁场 1T 10 G(gauss) 4 = 地磁场Bearth  510-5T SI unit: Tesla (T), Gauss or N/(Am). 单位 特斯拉 1(T) =1N/Am 2 Unit of Magnetic Field