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Vacuum permittivity

 

The physical constant ε0, commonly called the vacuum permittivity, permittivity of free space or electric constant, is an ideal, (baseline) physical constant, which is the value of the absolute dielectric permittivity of classical vacuum. Its value is:

                 ε0 = 8.854 187 817... x 10−12 [F/m] (farads per meter).

This constant relates the units for electric charge to mechanical quantities such as length and force. For example, the force between two separated electric charges (in the vacuum of classical electromagnetism) is given by Coulomb's law:

                            1          q1q2

                 Fc = _______  _______

                        4πε0       r^2

where q1 and q2 are the charges, and r is the distance between them. Likewise, ε0 appears in Maxwell's equations, which describe the properties of electric and magnetic fields and electromagnetic radiation, and relate them to their sources.

 

 

permittivity  誘電率

constant  定数

ideal  理想

absolute  絶対の

dielectric  絶縁体

likewise  同様に

property  財産

radiation  放熱        8

 

 

Maxwell's equations

 

Maxwell's equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electrodynamics, classical optics, and electric circuits. These fields in turn underlie modern electrical and communications technologies. Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents. They are named after the Scottish physicist and mathematician James Clerk Maxwell, who published an early form of those equations between 1861 and 1862.

The equations have two major variants. The "microscopic" set of Maxwell's equations uses total charge and total current, including the complicated charges and currents in materials at the atomic scale; it has universal applicability but may be unfeasible to calculate. The "macroscopic" set of Maxwell's equations defines two new auxiliary fields that describe large-scale behavior without having to consider these atomic scale details, but it requires the use of parameters characterizing the electromagnetic properties of the relevant materials.

The term "Maxwell's equations" is often used for other forms of Maxwell's equations. For example, space-time formulations are commonly used in high energy and gravitational physics. These formulations, defined on space-time rather than space and time separately, are manifestly compatible with special and general relativity. In quantum mechanics and analytical mechanics, versions of Maxwell's equations based on the electric and magnetic potentials are preferred.

Since the mid-20th century, it has been understood that Maxwell's equations are not exact laws of the universe, but are a classical approximation to the more accurate and fundamental theory of quantum electrodynamics. In most cases, though, quantum deviations from Maxwell's equations are immeasurably small. Exceptions occur when the particle nature of light is important or for very strong electric fields.

 

 

partial 部分的な

differential 差異

foundation  創設

electrodynamics 電気力学

optics 光学

underlie 下地

generated 生成された

altered 変更された

currents 電流

variant 変形
microscopic 微視的

complicate 複雑な

applicability 適用性
unfeasible 実施し難い

define 定義する

auxiliary 補助物
behavior 行動

consider  考える

require  要求する

property 財産
relevant 関連した

term 期間

form 形態

formulation 公式化

commonly 一般に

rather かなり

separately 別々に

manifestly 明白に

compatible 適合

general 一般

relativity 相対性

quantum 定量
analytical 分析的

potential 潜在的な

prefer ほうを好む

exact 正確

approximation 近似
accurate 正確

fundamental 基本

though しかし

deviation 偏差
immeasurably 計りがたいほど

exception 例外

occur 起こる

particle 粒子            43

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