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所在平台: Udemy |
课程主页: https://www.udemy.com/course/electromagnetism-physics-moving-charges-and-magnetism/
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**课程名称：** 电磁学物理 - 运动电荷与磁性 **课程概述：** 本课程深入探讨了运动电荷与磁性相关的物理学原理。主要内容包括： * **磁场概念：** 介绍磁场的由来，从奥斯特实验开始，展示电流如何产生磁场，并深入讲解毕奥-萨伐尔定律及其在圆形电流环的应用。 * **安培定则及应用：** 学习安培定则，并将其应用于计算长直导线、直形和环形螺线管的磁场。 * **洛伦兹力：** 理解洛伦兹力的概念，即电场力与磁场力之和，并分析其在匀强磁场和电场中对运动电荷的作用。 * **回旋加速器：** 学习回旋加速器的原理，即利用磁场使带电粒子在匀速圆周运动中加速。 * **磁场对电流的作用：** 探讨电流在磁场中受到的力，包括平行载流导线之间的作用力（安培单位的定义）以及载流导体在匀强磁场中的受力。 * **载流线圈的磁矩与受力：** 分析载流线圈在匀强磁场中的力矩，引入磁矩的概念，并详细介绍动圈式检流计的工作原理，包括其灵敏度和转换为电流表、电压表的方法。 **教学重点总结：** 1. **洛伦兹力：** 运动电荷 q 在磁场 **B** 和电场 **E** 中的总受力为 $F = q (v × B + E)$。其中磁场力 $q (v × B)$ 垂直于速度 $v$，不做功。 2. **载流导线受力：** 长度为 $l$、载有电流 $I$ 的直导线在匀强磁场 **B** 中受到的力为 $F = I l × B$。 3. **回旋加速器：** 粒子在垂直于磁场 **B** 的平面内做圆周运动，其运动频率（回旋频率）与粒子的速度和半径无关，这是回旋加速器加速粒子的原理。 4. **毕奥-萨伐尔定律：** 描述了电流元 $I dl$ 在距离 $r$ 处的磁感应强度 $dB$。 5. **长螺线管内部磁场：** 载有电流 $I$ 的长螺线管内部磁场大小为 $B = \mu_0 nI$，其中 $n$ 为单位长度的匝数。 6. **平行载流导线：** 同向电流相互吸引，反向电流相互排斥。 7. **载流线圈的磁矩与受力：** 具有 $N$ 匝、面积 $A$、载有电流 $I$ 的平面载流线圈具有磁矩 $m = NI A$，方向由右手螺旋法则确定。在匀强磁场 **B** 中，线圈受到的合外力为零，但存在力矩 $\tau = m × B$。动圈式检流计中，此力矩与弹簧的恢复力矩平衡，即 $k\phi = NI AB$。 8. **检流计的改装：** 动圈式检流计可通过并联小电阻（分流器）改装成电流表，串联大电阻改装成电压表。
Moving Charges and MagnetismConcept of magnetic field −Oersted's experimentBiot - Savart law and its application to current carrying circular loopAmpere's law and its applications to infinitely long straight wireStraight and toroidal solenoidsForce on a moving charge in uniform magnetic and electric fieldsCyclotronForce on a current-carrying conductor in a uniform magnetic fieldForce between two parallel current-carrying conductors-definition of ampereTorque experienced by a current loop in uniform magnetic field; moving coil galvanometer-its current sensitivity and conversion to ammeter and voltmeter.SUMMARY1. The total force on a charge q moving with velocity v in the presence of magnetic and electric fields B and E, respectively is called the Lorentz force. It is given by the expression: F = q (v × B + E) The magnetic force q (v × B) is normal to v and work done by it is zero. 2. A straight conductor of length l and carrying a steady current I experiences a force F in a uniform external magnetic field B, F = I l × B wherel = l and the direction of l is given by the direction of the current. 3. In a uniform magnetic field B, a charge q executes a circular orbit in a plane normal to B. Its frequency of uniform circular motion is called the cyclotron frequency. This frequency is independent of the particle's speed and radius. This fact is exploited in a machine, the cyclotron, which is used to accelerate charged particles. 4. The Biot-Savart law asserts that the magnetic field dB due to an element dl carrying a steady current I at a point P at a distance r from the current element5. The magnitude of the field B inside a long solenoid carrying a current I is B = µ0 nI.6. Parallel currents attract and anti-parallel currents repel.7. A planar loop carrying a current I, having N closely wound turns, and an area A possesses a magnetic moment m where, m = N I A and the direction of m is given by the right-hand thumb rule: curl the palm of your right hand along the loop with the fingers pointing in the direction of the current. The thumb sticking out gives the direction of m (and A) When this loop is placed in a uniform magnetic field B, the force F on it is: F = 0 And the torque on it is, τ = m × B In a moving coil galvanometer, this torque is balanced by a countertorque due to a spring, yielding kφ = NI AB. where φ is the equilibrium deflection and k the torsion constant of the spring.8. A moving coil galvanometer can be converted into a ammeter by introducing a shunt resistance r s , of small value in parallel. It can be converted into a voltmeter by introducing a resistance of a large value in series.
