麦克斯韦-法拉第方程

The Maxwell-Faraday equation is a fundamental law of electromagnetism that describes how a changing magnetic field generates an electric field. In its differential form, [latex]\nabla \times \mathbf{E} = -\frac{\partial \mathbf{B}}{\partial t}[/latex], it provides a localized, microscopic description of this phenomenon. Here, [latex]\nabla \times[/latex] is the curl operator, which measures the rotational tendency of a vector field. [latex]\mathbf{E}[/latex] represents the electric field, and [latex]\mathbf{B}[/latex] is the magnetic field. The term [latex]\frac{\partial \mathbf{B}}{\partial t}[/latex] is the partial derivative of the magnetic field with respect to time, signifying its rate of change at a specific point in space.

A key implication of this equation is that the induced electric field is non-conservative. A conservative vector field has a curl of zero, meaning the line integral around any 闭环 is zero. Since the curl of [latex]\mathbf{E}[/latex] is non-zero in the presence of a changing magnetic field, the work done by this electric field on a charge moving in a closed loop is not zero. This non-zero work per unit charge is precisely the 电动势 (EMF) that drives current in a conductor.

This equation was James Clerk Maxwell’s generalization of Michael Faraday’s experimental findings from 1831. Faraday observed that changing magnetic flux through a circuit induced a current, but he described it in terms of flux and EMF. Maxwell reformulated this observation into a local field equation, making it a cornerstone of his unified theory of electromagnetism. It elegantly connects electricity and magnetism, showing they are not separate phenomena but two facets of a single electromagnetic field. This formulation is crucial for deriving the wave equation for electromagnetic radiation, predicting the existence of light waves, radio waves, and other forms of electromagnetic energy propagating through space.