A system of units with the meter (m) for length, the kilogram (kg) for mass, the second (s) for time, and the ampere (A) for current as base units. The practical units of electromagnetic quantities, such as the volt (V), ampere, and ohm (Ω), are either too large or too small for the CGS units, but they are coherent units (→ physical units) for the rationalized MKS units, as pointed out by G. Giorgi in 1901. Giorgi proposed the MKSΩ system of units, adopting the ohm as the base unit representing electromagnetic quantities, but later, for measurement reasons, the MKSA system of units, which uses the ampere as the base unit instead of the ohm, came to be used. This MKSA system of units is a theoretically consistent and coherent system of units, and has units of appropriate size, making it convenient in practice. Moreover, it simplifies electromagnetic calculations, so it has gradually become widely used. Furthermore, three base units were added to the SI system to include all physical quantities, forming the International System of Units. Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information |
基本単位として長さにメートル (m) ,質量にキログラム(kg),時間に秒 (s) ,電流にアンペア (A) をもつ単位系。電磁気量の実用単位ボルト (V) ,アンペア,オーム (Ω) などは,CGS単位に対して過大または過小の値をとるが,有理化された MKS単位に対してはコヒーレントな単位 (→物理単位 ) になっていることが 1901年 G.ジョルジによって指摘された。ジョルジは電磁気量を代表する基本単位としてオームを採用して MKSΩ 単位系を提案したが,そののち計測上の理由からオームの代りにアンペアを基本単位とする MKSA単位系が用いられるようになった。この MKSA単位系は理論的に一貫性をもつコヒーレントな単位系で,適当な大きさの単位量をもつので,実用上も便利である。しかも電磁気の計算を簡略化させるので,次第に広く使用されるようになった。さらに,3つの基本単位を加えて,すべての物理量の単位を包括するように整備したのが国際単位系SIである。
出典 ブリタニカ国際大百科事典 小項目事典ブリタニカ国際大百科事典 小項目事典について 情報 |
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