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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Four-current ： ウィキペディア英語版 Four-current In special and general relativity, the four-current is the four-dimensional analogue of the electric current density, which is used in the geometric context of ''four-dimensional spacetime'', rather than three-dimensional space and time separately. Mathematically it is a four-vector, and is Lorentz covariant. Analogously, it is possible to have any form of "current density", meaning the flow of a quantity per unit time per unit area, see current density for more on this quantity. This article uses the summation convention for indices, see covariance and contravariance of vectors for background on raised and lowered indices, and raising and lowering indices on how to switch between them. ==Definition== Using the Minkowski metric $\backslash eta\_$ of metric signature (+−−−), its four components are given by: :$J^\backslash alpha\; =\; \backslash left(c\; \backslash rho,\; j^1\; ,\; j^2\; ,\; j^3\; \backslash right)\; =\; \backslash left(c\; \backslash rho,\; \backslash mathbf\; \backslash right)$ where ''c'' is the speed of light, ''ρ'' is the charge density and j the conventional current density. The dummy index ''α'' labels the spacetime dimensions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Four-current」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.