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Eddy Currents (Foucault’s Currents)

1851

Léon Foucault

（图片仅供参考）

Eddy currents are loops of electrical current induced within bulk conductors by a changing magnetic field, in accordance with Faraday’s law. They flow in closed loops in planes perpendicular to the magnetic field. Following Lenz’s law, these currents create their own magnetic field that opposes the change in the external flux, causing a repulsive or drag force and resistive heating.

当固体金属导体在磁场中运动或暴露于时变磁场中时，其内部的自由电子会受到磁场的影响。洛伦兹力从而使它们循环流动。这些旋转的电流称为涡流。涡流的大小与磁场强度、线圈面积和磁通量变化率成正比，与材料的电阻率成反比。以热能形式耗散的能量（P = I²R）可能相当大，感应加热正是利用了这一效应。

In many applications, such as transformer and motor cores, eddy currents are undesirable as they represent a significant energy loss (core loss). To mitigate this, the cores are constructed from thin, laminated sheets of a ferromagnetic material like silicon steel, with each sheet electrically insulated from the next. This lamination breaks up the large conductive paths, forcing the eddy currents into much smaller, higher-resistance loops, thereby drastically reducing the energy lost to heat.

Electrical Conductance, Electrical Engineering, Electromagnetism, Non-Destructive Testing (NDT)

UNESCO Nomenclature: 2205

– Electricity and magnetism

类型

Physical Phenomenon

中断

Revolutionary

用法

广泛使用

前体

Faraday’s law of induction
Lenz’s law
Ohm’s law
洛伦兹力的发现

应用程序

火车和过山车的涡流制动器
炉子和炉灶的感应加热
金属探测器
材料无损检测
机械仪表中的阻尼
接近传感器

专利：

潜在创新理念

contactless 粘度 measurement for industrial fluids
小型水下航行器涡流推进系统
集成涡流图案的自加热炊具
采用受控涡流排斥的磁悬浮系统
通过感应电流进行非侵入性血流监测
利用纳米粒子和涡流进行靶向热疗癌症治疗
精密机械主动阻尼系统
基于涡流的假币检测系统
material 排序 systems that differentiate alloys based on conductivity
非接触式高扭矩磁力齿轮

Related to: Eddy currents, Foucault’s currents, induction heating, Eddy current brake, non-destructive testing, Lenz’s law, Faraday’s law, electromagnetism, resistive heating, Léon Foucault.

历史背景

Chemist conducting experiments with catalysts in a vintage laboratory setting, 1850.

化学平衡催化剂

催化剂通过提供活化能较低的替代反应途径，平等地提高正向和逆向反应的速率。虽然催化剂可以使体系更快地达到平衡，但它不会改变平衡本身的位置。反应物和产物的平衡浓度以及平衡常数K的值保持不变。

19th-century chemist measuring gas volumes illustrating the Ideal Gas Law in thermodynamics.

理想气体定律（摩尔形式）

The ideal gas law is the equation of state for a hypothetical ideal gas, approximating the behavior of many gases under various conditions. The molar form relates pressure ([latex]P[/latex]), volume ([latex]V[/latex]), amount of substance in moles ([latex]n[/latex]), and absolute temperature ([latex]T[/latex]) via the universal gas constant ([latex]R[/latex]): [latex]PV = nRT[/latex].

Laboratory apparatus for measuring vapor pressure and temperature in thermodynamics.

克劳修斯-克拉珀龙关系

The Clausius-Clapeyron relation describes the relationship between pressure and temperature for a substance at a phase transition, such as liquid and vapor. For water vapor, it shows that saturation vapor pressure increases exponentially with temperature. The approximate form is [latex]\frac{dp}{dT} = \frac{L}{T(V_v - V_l)} \approx \frac{L p}{R_v T^2}[/latex], where L is latent heat.

Eddy Currents (Foucault’s Currents)

Thermodynamic laboratory with Peltier and Seebeck apparatus illustrating Kelvin relations.

开尔文（汤姆森）关系公司

The Kelvin relations are two equations that thermodynamically link the three thermoelectric coefficients: the first relation connects the Peltier coefficient ([latex]\Pi[/latex]) to the Seebeck coefficient ([latex]S[/latex]) via absolute temperature ([latex]T[/latex]): [latex]Pi = S \cdot T[/latex]. The second relates the Thomson coefficient ([latex]\mathcal{K}[/latex]) to the temperature derivative of the Seebeck coefficient: [latex]\mathcal{K} = T \frac{dS}{dT}[/latex].

Lead-acid battery with lead and lead dioxide electrodes in sulfuric acid electrolyte, electrochemistry.

铅酸电池

铅酸电池是第一种可充电电池，由加斯顿·普兰特于1859年发明。它使用浸入硫酸（H₂SO₄）电解液中的铅（Pb）阳极和二氧化铅（PbO₂）阴极来工作。放电时，两个电极都会转化为硫酸铅（PbSO₄），充电时则发生逆转，从而实现能量的储存和重复利用。

Laboratory setup illustrating the Maxwell-Faraday Equation in electromagnetism.

麦克斯韦-法拉第方程

This is the differential form of Faraday's law of induction, one of Maxwell's four equations. It states that a time-varying magnetic field ([latex]\mathbf{B}[/latex]) always accompanies a spatially varying, non-conservative electric field ([latex]\mathbf{E}[/latex]). The relationship is expressed as [latex]\nabla \times \mathbf{E} = -\frac{\partial \mathbf{B}}{\partial t}[/latex]. This equation governs how changing magnetic fields create electric fields at a specific point in space.

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Engineers designing an efficient heat engine in a laboratory, illustrating thermodynamics applications.

热力学第二定律

第二定律引入了熵的概念，并定义了自发过程的方向。它有多种表述方式，但一个关键结论是，孤立系统的总熵永远不会随时间减少。这条定律解释了“时间之箭”以及为什么过程不可逆，例如热量自发地从热物体流向冷物体。

Laboratory scene illustrating thermodynamic experiments on the Perfect Gas Model.

完美的气体模型

A perfect gas is a theoretical model of a gas where intermolecular forces are neglected and specific heat capacities ([latex]C_P[/latex] and [latex]C_V[/latex]) are assumed to be constant with respect to temperature. This simplifies thermodynamic calculations significantly. It is a specific case of the ideal gas, where specific heats can vary with temperature, making it a more constrained model.

19th-century laboratory scene with Ludwig Boltzmann studying the Ideal Gas Law in statistical thermodynamics.

理想气体定律（统计形式）

The statistical mechanics formulation of the ideal gas law expresses the relationship in terms of the microscopic properties of the gas. It relates pressure ([latex]P[/latex]) and volume ([latex]V[/latex]) to the total number of particles ([latex]N[/latex]) and the absolute temperature ([latex]T[/latex]) through the Boltzmann constant ([latex]k_B[/latex]): [latex]PV = Nk_BT[/latex].

Current-carrying conductor experiment demonstrating Thomson Effect in thermoelectricity.

汤姆森效应

The Thomson effect describes the heating or cooling of a current-carrying conductor when a temperature gradient exists along its length. Heat is produced or absorbed when current flows through a material with a temperature gradient. The rate of heat production per unit length is given by [latex]\frac{dQ}{dx} = -\mathcal{K} J \frac{dT}{dx}[/latex], where [latex]\mathcal{K}[/latex] is the Thomson coefficient.

Laboratory apparatus demonstrating the Joule-Thomson effect in thermodynamics.

焦耳-汤姆逊效应

焦耳-汤姆逊（或焦耳-开尔文）效应描述的是实际气体在保持绝缘的情况下，被迫通过阀门或多孔塞（即等焓过程）时的温度变化。在给定压力下，气体具有反转温度。如果气体膨胀至低于该温度，则会冷却；如果气体膨胀至高于该温度，则会升温。这种冷却效应是现代制冷和液化技术的基石。

Lead-acid battery with lead anode and lead dioxide cathode in a historical lab setting.

铅酸电池化学

首款商业化成功的可充电电池。它采用铅 (Pb) 阳极、二氧化铅 (PbO₂) 阴极和硫酸 (H₂SO₄) 电解质。放电过程中，两个电极均转化为硫酸铅 (PbSO₄)，并消耗硫酸。该过程可通过施加外部电流实现化学可逆，使其成为一种实用且可靠的储能系统。

Laboratory setup for measuring molar volume of gas in physical chemistry experiments.

气体摩尔体积

阿伏伽德罗定律的直接推论是摩尔体积的概念：在特定温度和压强下，任何理想气体的1摩尔体积都固定不变。在标准温度和压强 (STP)（定义为273.15 K (0 °C) 和1个大气压）下，该体积约为22.4升。该原理简化了化学计量学，允许气体体积与摩尔之间的直接换算。

Gauss’s Law for Magnetism

One of the four Maxwell's equations, Gauss's law for magnetism states that the net magnetic flux out of any closed surface is zero. This is expressed mathematically as [latex]\oint_S \vec{B} \cdot d\vec{A} = 0[/latex]. This law is a statement of the experimental observation that magnetic monopoles (isolated north or south poles) have never been detected. Magnetic field lines always form closed loops.

（如果日期未知或不相关，例如“流体力学”，则提供其显著出现的近似估计）