Magnetic field

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  • Magnetic Field
definition
  • Pertaining to the magnetic field generated by the Earth, consisting of both the dipole and non-dipole components.
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Abstract from DBPedia
    A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. A permanent magnet's magnetic field pulls on ferromagnetic materials such as iron, and attracts or repels other magnets. In addition, a nonuniform magnetic field exerts minuscule forces on "nonmagnetic" materials by three other magnetic effects: paramagnetism, diamagnetism, and antiferromagnetism, although these forces are usually so small they can only be detected by laboratory equipment. Magnetic fields surround magnetized materials, and are created by electric currents such as those used in electromagnets, and by electric fields varying in time. Since both strength and direction of a magnetic field may vary with location, it is described mathematically by a function assigning a vector to each point of space, called a vector field. In electromagnetics, the term "magnetic field" is used for two distinct but closely related vector fields denoted by the symbols B and H. In the International System of Units, the unit of H, magnetic field strength, is the ampere per meter (A/m). The unit of B, the magnetic flux density, is the tesla (in SI base units: kilogram per second2 per ampere), which is equivalent to newton per meter per ampere. H and B differ in how they account for magnetization. In vacuum, the two fields are related through the vacuum permeability, ; but in a magnetized material, the quantities on each side of this equation differ by the magnetization field of the material. Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. Magnetic fields and electric fields are interrelated and are both components of the electromagnetic force, one of the four fundamental forces of nature. Magnetic fields are used throughout modern technology, particularly in electrical engineering and electromechanics. Rotating magnetic fields are used in both electric motors and generators. The interaction of magnetic fields in electric devices such as transformers is conceptualized and investigated as magnetic circuits. Magnetic forces give information about the charge carriers in a material through the Hall effect. The Earth produces its own magnetic field, which shields the Earth's ozone layer from the solar wind and is important in navigation using a compass.

    磁場（じば、英語: Magnetic field）は、電気的現象・磁気的現象を記述するための物理的概念であり、電流が作り出す場として定義される。工学分野では、磁界（じかい）ということもある。 単に磁場と言った場合は磁束密度Bもしくは、「磁場」Hのどちらかを指すものとして用いられるが、どちらを指しているのかは文脈により、また、どちらの解釈としても問題ない場合も多い。後述のとおりBとHは一定の関係にあるが、BとHの単位は国際単位系（SI）でそれぞれWb/m2, A/m であり、次元も異なる独立した二つの物理量である。Hの単位はN/Wbで表すこともある。なお、CGS単位系における、磁場 Hの単位は、Oeである。この項では一般的な磁場の性質を扱うこととする。 磁場は、空間の各点で向きと大きさを持つ物理量（ベクトル場）であり、電流によって形成される。磁場の大きさは、+1のN極が受ける力の大きさで表される。磁場を図示する場合、N極からS極向きに磁力線の矢印を描く。 小学校などの理科の授業では、砂鉄が磁石の周りを囲むように引きつけられる現象をもって、磁場の存在を教える。このことから、磁場の影響を受けるのは鉄だけであると思われがちだが、強力な磁場の中では、様々な物質が影響を受けることが分かっている。最近では、磁場や電場（電磁場、電磁波）が生物に与える影響について関心が寄せられている。

    (Source: http://dbpedia.org/resource/Magnetic_field)
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