E12电流的磁场2.ppt

* Chapter 12-2 Magnetic Force on Currents 12.6 Magnetic force on currents Ampere’s law 12.7 Magnetic field acts on a loop of wire 12.8 The work of magnetic force 12.9 Lorentz force 12.10 Charged particle moving in electric and magnetic field 12.11 Hall effect 12.6 Magnetic force on current Ampere’s law 1 Experiment 实验现象 A current-carrying wire in a magnetic field experience a force： If wire is perpendicular to B，the force：F = IBL； If wire is parallel to B，the force： F = 0； If the angle between wire and B isα, the force: F = IBLsinα Force direction is determined by left hand rule. 2 Ampere’s law Magnitude： Direction： Force on total current: 3 Examples a ?0 I1 I2 The field by wire(I1) at wire(I2): ? Magnetic force on current element Direction as shown in Fig The force per unit length wire 取a=1m, f=2?10-7 N/m, I=1A Parallel wires carrying current in the same direction attract one another Ex 1 determine the force between two parallel straight wires I1，I2，?0，a Ex 2 determine the force on a semicircular section of wire of radius R carrying a current I in a magnetic field. Discuss (1) The force on rigid circular wire Corollary: 任一段弯曲载流导线在均匀磁场中所受的磁场作用力，等于从起点到终点连接的直导线通过相同的电流时所受的作用力。 (2) 刚性1/4 圆线圈受力 (3) 连接两端点的直线电流受力 方向: 与x轴夹角?/4 y x O I 例3 求一载流导线框在无限长直导线磁场中的受力和运动趋势 解 1 2 3 4 1 3 方向向左 方向向右 2 4 整个线圈所受的合力 ? 线圈向左做平动 × × × × x 例4 匀强磁场中，平行于磁场线插入一无限大载流平面,放入后平面两侧的磁感应强度分别为 求 载流平面上单位面积所受的磁场力？ 和 如图所示。 解 ?无限大载流平面所产生的磁场 ? 磁场叠加原理 取坐标系如图 —— 平板电流密度 Ex 5 Two current-carrying wires is shown in Fig (MN is coplanar with wire I1). Calculate the force on wire MN. Magnetic force on current element I2dl： Magnetic force on MN: The field by current I1 at current I2: Direction down into page Direction: as shown in the Fig M F x I2dl 300 a N I1 b 例 6 半径为 载有电流 的导体圆环与电流为 的长直导线 放在同一平面内（如图），直导线与圆心相距为 d ，且 R d 两者间绝缘 , 求 作用在圆电流上的磁场力. O d R . 解 O d R . 12.7 Magnetic field acts on a loop of wire a b c d ad=bc=l1