标题： 电磁感应的一般定律 显示英文标题

标题： A general law for electromagnetic induction

摘要： 由单位正电荷在闭合回路上受到的洛伦兹力的积分定义的感应$emf$立即导出了电磁感应现象的一般定律。 该一般定律应用于三个重要的情况：移动的杆、法拉第盘和科宾诺盘。 最后一个应用说明了电荷的漂移速度对感应$emf$的贡献：在不使用电导的微观模型的情况下得到了磁阻效应。 麦克斯韦写下了“电动势强度的一般方程”，如果正确解释其中出现的速度，这些方程在闭合回路上积分即可得到电磁感应的一般定律。 通过任意具有电路为边界的表面的磁场通量{\em 不是原因}是感应$emf$的。 当电路是细丝状时，通量定律应被视为预测感应$emf$值的计算捷径。 最后，电磁感应的一般定律在由磁体和作相对匀速运动的电路组成的系统的两个参考系中都给出了感应$emf$，这符合狭义相对论的要求。 显示英文摘要

摘要： The definition of the induced $emf$ as the integral over a closed loop of the Lorentz force acting on a unit positive charge leads immediately to a general law for electromagnetic induction phenomena. The general law is applied to three significant cases: moving bar, Faraday's and Corbino's disc. This last application illustrates the contribution of the drift velocity of the charges to the induced $emf$: the magneto-resistance effect is obtained without using microscopic models of electrical conduction. Maxwell wrote down `general equations of electromotive intensity' that, integrated over a closed loop, yield the general law for electromagnetic induction, if the velocity appearing in them is correctly interpreted. The flux of the magnetic field through an arbitrary surface that have the circuit as contour {\em is not the cause} of the induced $emf$. The flux rule must be considered as a calculation shortcut for predicting the value of the induced $emf$ when the circuit is filiform. Finally, the general law of electromagnetic induction yields the induced $emf$ in both reference frames of a system composed by a magnet and a circuit in relative uniform motion, as required by special relativity.