电磁感应的通量法则与场方程

电磁感应的通量法则是一条在电路近似下成立的经验规律。结合电磁场的观念,可以得到麦克斯韦方程组中法拉第电磁感应定律的积分和微分形式;它是比通量法则更为基本的电磁规律。考虑电磁规律的相对论不变性,本文修正了电动势的定义和计算公式,并得到通量法则的“低速小尺寸”极限。     

麦克斯韦电磁场理论思想体系的科学美

 人类在很早就已经发现了电现象和磁现象,并为揭开它们神秘的面纱而作出了不懈的努力。１９世纪初,人们发现各种自然现象之间有其内在的关联性,另一方面,在法国古典哲学关于自然界统一思想的影响下,部分自然科学家开始寻求电与磁的联系,在科学与美学的融合中不断升华,深刻了人们对电、磁的认识,同时也在充实和完善着科学家们自己的物理美学理念。在这一漫长的认识过程中,科学家们逐渐建立了相当完备的电和磁的理论,为完成电磁的统一扫清了主要的障碍。这其中,尤以库仑定律、高斯定律、法拉第电磁感应定律和安培定律这四大定律影响巨大,为电磁学取得突破性的进展奠定了坚实的基础。     

伦琴对电磁理论的重要贡献

提到伦琴，人们往往想到的是他对X射线的发现，而对他在电磁理论方面的重要贡献则较少提及．文章详细叙述了伦琴为论证“位移电流”存在而做的实验，此实验曾被誉为是19世纪最重要的物理实验之一，在当时广受赞誉，但今天却被人们渐渐遗忘了．希望该文能够使人们对伦琴为构建19世纪物理学宏伟大厦而取得成就的重要性有更深入的认识。     

利用可拆交流演示变压器验证法拉第电磁感应定律

利用长闭合导线代替演示变压器的副线圈，设计了验证法拉第电磁感应定律实验．     

关于真空中的位移电流、Maxwell方程组、电磁场的源及Jefimenko公式的几点注记

通过分析指出：电磁场是一个不可分割的整体，Maxwell方程组是电磁场的运动方程，电磁场的源是电荷与电流的分布，Jefimenko公式是真空中Maxwell方程组的解。     

涡电流电磁感应演示仪的设计

以一个新的角度--涡电流效应演示电磁感应现象.演示仪器引入气垫导轨,由悬挂的钕铁硼永磁铁与铝板小车在接近无外界阻力的状态下相互作用来演示动生电动势现象;由高频交流电磁铁加热铝板小车或点亮接有线圈的小灯泡演示感生电动势现象.     

麦克斯韦方程组的建立及其作用

麦克斯韦提出了描述经典电磁场运动及其与带电粒子相互作用规律的完备方程组,将电学、磁学和光学统一为电磁场动力学理论。这一理论具有洛仑兹协变性和U(1)局域规范不变性,成为构造粒子物理标准模型的经典模板,在物理理论和实验发展中起着不可估量的巨大作用。     

Analytical solutions to the electromagnetic field in a cylindrical shell excited by external axial current

The solutions to the electromagnetic field excited by a long axial current outside a conductive and magnetic cylindrical shell of finite length are studied in this paper. The more accurate analytical solutions are obtained by solving the proper boundary value problems by the separation variable method. Then the solutions are simplified according to asymptotic formulas of Bessel functions. Compared with the accurate solutions, the simplified solutions do not contain the Bessel functions and the inverse operation of the singular matrix, and can be calculated out fast by computers. The simplified solutions are more suitable for the cylindrical shell of high permeability and conductivity excited by a high frequency source. Both of the numerical results and the physical experimental results validate the simplified solutions obtained.     

A solution to the problem of the skin effect with a bias current in the Maxwell plasma by the method of expansion in eigenfunctions

A problem of the skin effect in the Maxwell plasma is solved analytically by the method of expansion in eigenfunctions based on the Vlasov–Maxwell kinetic equation with a self-consistent electric field. Specular electron reflection from the boundary is used as a boundary condition. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 33–38, February, 2009.     

Prediction and experimental measurement of the electromagnetic thrust generated by a microwave thruster system

A microwave thruster system that can convert microwave power directly to thrust without a gas propellant is developed. In the system, a cylindrical tapered resonance cavity and a magnetron microwave source are used respectively as the thruster cavity and the energy source to generate the electromagnetic wave. The wave is radiated into and then reflected from the cavity to form a pure standing wave with non-uniform electromagnetic pressure distribution. Consequently, a net electromagnetic thrust exerted on the axis of the thruster cavity appears, which is demonstrated through theoretical calculation based on the electromagnetic theory. The net electromagnetic thrust is also experimentally measured in the range from 70 mN to 720 mN when the microwave output power is from 80 W to 2500 W.     

圆电流磁感线的分布及磁感应强度的函数表达式

从圆电流的矢势出发,导出了其磁感线所满足的方程,运用数学软件MatLab绘出了其磁感线的分布图.然后用公式B=Δ×A求出了圆电流在空间任意点磁感应强度的函数表达式,并图示了其变化情况.     

On the relationship between the lightning electromagnetic field and the channel-base current based on the TL model

A set of approximation expressions relating the lightning channel-base current and the lightning electric and magnetic fields on earth surface are proposed respectively in the near-zone and far-zone, by employing the transmission line (TL) model. The derived expressions show that, the electric and magnetic fields waveforms can be expressed approximately by the channel-base current waveform with different factors at a certain distances, whether in the near-zone or far-zone. The factors can be expressed in terms of the return stroke wavefront speed v, the speed of light c, and the horizontal distance r between the return-stroke channel and the observation point.