Concept

# Electromagnetic tensor

Summary
In electromagnetism, the electromagnetic tensor or electromagnetic field tensor (sometimes called the field strength tensor, Faraday tensor or Maxwell bivector) is a mathematical object that describes the electromagnetic field in spacetime. The field tensor was first used after the four-dimensional tensor formulation of special relativity was introduced by Hermann Minkowski. The tensor allows related physical laws to be written very concisely, and allows for the quantization of the electromagnetic field by Lagrangian formulation described below. The electromagnetic tensor, conventionally labelled F, is defined as the exterior derivative of the electromagnetic four-potential, A, a differential 1-form: Therefore, F is a differential 2-form—that is, an antisymmetric rank-2 tensor field—on Minkowski space. In component form, where is the four-gradient and is the four-potential. SI units for Maxwell's equations and the particle physicist's sign convention for the signature of Minkowski space (+ − − −), will be used throughout this article. The Faraday differential 2-form is given by This is the exterior derivative of its 1-form antiderivative where has ( is a scalar potential for the irrotational/conservative vector field ) and has ( is a vector potential for the solenoidal vector field ). Note that where is the exterior derivative, is the Hodge star, (where is the electric current density, and is the electric charge density) is the 4-current density 1-form, is the differential forms version of Maxwell's equations. The electric and magnetic fields can be obtained from the components of the electromagnetic tensor. The relationship is simplest in Cartesian coordinates: where c is the speed of light, and where is the Levi-Civita tensor. This gives the fields in a particular reference frame; if the reference frame is changed, the components of the electromagnetic tensor will transform covariantly, and the fields in the new frame will be given by the new components.