测定平行电流间的磁场力

两根平行的长直导线,通以电流时,它们之间的磁相互作用力为式中,I1、I2分别为流过两导线中的电流;d为两导线的间距. 本实验将两根直径为0.140毫米,长为200毫米,表面很光滑的磷铜丝,平行固定在导线架上,见图1,架子四周有调节螺丝可调整导线的平行及间距.由于实验中两导线的间距调得较小(因导线外有漆包着,可避免相碰而造成短路),可用作光学衍射实验中的单缝.另将一激光光束射在此单缝上,整个实验装置见图2.当两长直导线上通过一定的、方向相同或相反的电流时,由于电流与磁场的作用,两导线之间可产生相斥或相吸的现象,而当电流变化时,随之引…     

计算感生电动势的角度法

局限于圆柱形空间、方向平行于圆柱轴线的均匀磁场随时间均匀变化时，在周围空间激发感生电场。处于该电场中的有限长直导线上产生的感生电动势可由简捷方法求出。本文根据电动势的定义导出计算直导线上感生电动势的角度法。     

任意形状磁场区域感生电动势的研究

讨论任意形状磁场区域所产生的感生电动势的计算方法.首先讨论有限长直导线的情况.然后以圆形、矩形和三角形磁场区域为例来计算,结果表明不同形状的磁场区域对相同长度直导线所产生的感生电动势也不相同.其次研究了磁场对无限长直导线所产生的感生电动势.证明了磁场对无限长直导线所产生的感生电动势仅仅依赖磁场区域的面积大小而与磁场区域的具体形状和导线到磁场的距离等因素无关.     

载流长直密绕螺线管磁场的全空间解

很多《普通物理学》教材讲到稳恒磁场时，都以长直密绕螺线管为例，为求解其磁场分布，一般都假设导线很细，将长直密绕螺线管简化为一串共轴圆电流，得到管内磁场是一均匀磁场，管外磁场为零的结论．但这样的螺线管模型不可能使电流从管的一端流到另一端，与实际情况相差较远．本文在不做这种简化假设的条件下，求得长直密绕螺线管磁场在全空间的精确解．ｌ长直密绕螺线管的磁场 设长直密绕螺线管的半径为Ｒ，单位长度上的匝数为ｎ，电流环绕轴线流动并与轴线方向成一角度ａ，如图１所示．将管上任一段的管壁展开，如图２（为清楚起见，图…     

长导线的反向电场

本文讨论了一根电流均匀增长的无限长直导线激发的电场．由于考虑了场是以光速传播的，在导线上有电荷的积累．得出的结果是：沿轴向电场分量为零，沿径向电场分量为 这与同轴电缆及传输线的情况是一致的．     

两条互靠直导线间的磁场力测定

两条互靠直导线间距微小，不易测准，本文介绍了一种用衍射法测定两条互靠长直导线间距的方法，并由此求出它们之间的磁场力大小。     

线圈在无限长载流直导线磁场中的逃逸速度研究

分析矩形、圆形线圈在无限长载流直导线磁场中的运动，求解线圈运动的感应电流和安培力，建立运动学微分方程，得到线圈在无限长载流直导线磁场中存在逃逸速度.线圈能从磁场中逃逸的最小初速度与线圈尺寸、电阻、初始位置、长直导线电流均有关，该模型为教师教学提供理论分析.     

读者来信（二）

读者来信（二）《大学物理》１９９５年第三期发表了《长直导线通以变化电流产生的涡旋电场》一文（以下简称苏文），该文在似稳条件下得出解式但此式给出的只是空间任意一点相对于ｒ＝１处的相对涡旋电场强度．苏文却认为它就是该电流的涡旋电场分布式，并用它计算电流附...     

关于电磁场的统一性和相对性

学过电场和磁场后,容易把二者看成本质不同的两回事。为了让学生们对电磁场的统一性和相对性有个粗浅的了解,我用两节课讲了下面一个常见问题。 一、问题的提出 如图1所示,一带正电q的粒子正以速度υ平行于强度为I的长直导线运动,该粒子距导线为r。在地面上(简称实验室系K)会观测到强度为 B=的磁场,方向沿图1中y轴正向。按洛仑兹公式,粒子所受磁场力为方向沿图1中z轴正向。因稳恒载流导线为电中性,周围不存在电场。 当在随同粒子一起运动的坐标系(简称粒子系K’)中观测时,会不会观测到力?如能观测到,那它是什么性质的力?它是否等于实验室…     

长直导线通以变化电流产生的涡旋电场

本文对长直导线通以变化电流时所产生的涡旋电场作了分析，给出涡旋电场分布公式，并通过例题对应用该式计算有关感生电动势作了说明．     

含时库仑势和线性势的薛定谔方程的求解

利用Burgan等人的时空变换方法对一类特殊形式的具有含时库仑势加线性项的薛定谔方程进行了分析和计算,并进一步讨论了更普遍形式的含时势V(r,t)=–a0ξ12r+nk=1akrkξk2+1(其中ξ=at2+bt+c,a0,a1,a2,…,an,a,b,c是满足一定关系的常数)的波函数     

现代核子-核子势

核子-核子二体相互作用是联结 QCD与核多体理论计算的桥梁,一直是核物理研究的主线之一.简单回顾了现代核子-核子相互作用理论的新发展,特别是在同位旋相关性方面.Nucleon nucleon interaction is the key point of nuclear physics, bridging the gap between QCD and the effective interaction appropriate for nuclear many body calculations. The older potential models are no longer suitable for describing the present set of more numerous and much more accurate experimental data without refitting the parameters. In 1990s, both older (classical) phenomenological potentials and meson exchange potentials have already had ...     

The Chemical Potential

The definition of the fundamental quantity, the chemical potential, is badly confused in the literature: there are at least three distinct definitions in various books and papers. While they all give the same result in the thermodynamic limit, major differences between them can occur for finite systems, in anomalous cases even for finite systems as large as a cm³. We resolve the situation by arguing that the chemical potential defined as the symbol μ conventionally appearing in the grand canonical density operator is the uniquely correct definition valid for all finite systems, the grand canonical ensemble being the only one of the various ensembles usually discussed (microcanonical, canonical, Gibbs, grand canonical) that is appropriate for statistical thermodynamics, whenever the chemical potential is physically relevant. The zero–temperature limit of this μ was derived by Perdew et al. for finite systems involving electrons, generally allowing for electron–electron interactions; we extend this derivation and, for semiconductors, we also consider the zero–T limit taken after the thermodynamic limit. The enormous finite size corrections (in macroscopic samples, e.g. 1 cm³) for one rather common definition of the c.p., found recently by Shegelski within the standard effective mass model of an ideal intrinsic semiconductor, are discussed. Also, two very–small–system examples are given, including a quantum dot.     

Inflation Without Potential

Due to the importance of inflation, considerable effort has gone into developingdifferent inflationary scenarios. In most of them inflation is driven by aself-interacting scalar field. Here we discuss an alternative way to implement aninflationary stage provided by noncanonical kinetic terms in the action for thescalar field.     

Relativistic Scattering States of Coulomb Potential Plus a New Ring-Shaped Potential

In this paper, exact solutions of scattering states of the Klein-Gordon equation with Coulomb potential plus a new ring-shaped potential are studied under the condition that the scalar potential is equal to the vector potential. The normalized wave functions of scattering states on the “k/2π scale” and the calculation formula of phase shifts are presented. Analytical properties of the scattering amplitude are discussed.     

Solution of Klein-Gordon Equation for Pseudo-Coulomb Potential Plus a New Ring-Shaped Potential

Under the condition of an equal mixing of vector and scalar potentials, exact solutions of bound states of the Klein-Gordon equation with pseudo-Coulomb potential plus a new ring-shaped potential are presented. Simultaneously, energy spectrum equations are also obtained. It is shown that the radial equation and angular wave functions are expressed by confluent hypergeogetric and hypergeogetric functions respectively.     

变形对称双阱势

利用变形双曲函数,将对称双阱势推广为变形对称双阱势模型.证明了该势模型是五参量指数型势模型的特例.运用超对称WKB近似和五参量指数型势模型的能谱公式,获得了变形对称双阱势模型的能谱公式.     

Potential models for quarkonia

In this paper I discuss what we can learn about quarkonium dissociation from lattice-potential based models. Special emphasis is given to results obtained in agreement by different models, and to the relevance of lattice QCD for potential models. Future directions are also discussed.