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# magnetic field

1. a region of space near a magnet, electric current, or moving charged particle in which a magnetic force acts on any other magnet, electric current, or moving charged particle.
[1835-45]

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Region around a magnet, electric current, or changing electric field in which magnetic forces are observable.

The field around a permanent magnet or wire carrying a steady direct current is stationary, while that around an alternating current or changing direct current is continuously changing. Magnetic fields are commonly represented by continuous lines of force, or magnetic flux, that emerge from north-seeking magnetic poles and enter south-seeking poles. The density of the lines indicates the magnitude of the field, the lines being crowded together where the magnetic field is strong. The SI unit for magnetic flux is the weber.

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region in the neighbourhood of a magnet, electric current, or changing electric field, in which magnetic forces (magnetic force) are observable. Magnetic fields such as that of the Earth cause magnetic compass needles and other permanent magnets to line up in the direction of the field. Magnetic fields force moving, electrically charged particles in a circular or helical path. This force—exerted on electric currents in wires in a magnetic field—underlies the operation of electric motors.

Around a permanent magnet or a wire carrying a steady electric current in one direction, the magnetic field is stationary and referred to as a magnetostatic field. At any given point its magnitude and direction remain the same. Around an alternating current or a fluctuating direct current, the magnetic field is continuously changing its magnitude and direction.

Magnetic fields may be represented by continuous lines of force or magnetic flux that emerge from north-seeking magnetic poles (magnetic pole) and enter south-seeking magnetic poles. The density of the lines indicates the magnitude of the magnetic field. At the poles of a magnet, for example, where the magnetic field is strong, the field lines are crowded together, or more dense. Farther away, where the magnetic field is weak, they fan out, becoming less dense. A uniform magnetic field is represented by equally spaced parallel straight lines. The direction of the flux is the direction in which the north-seeking pole of a small magnet points. The lines of flux are continuous, forming closed loops. For a bar magnet, they emerge from the north-seeking pole, fan out and around, enter the magnet at the south-seeking pole, and continue through the magnet to the north pole, where they again emerge. The SI unit for magnetic flux is the weber. The number of webers is a measure of the total number of field lines that cross a given area.

Magnetic fields may be represented mathematically by quantities called vectors that have direction as well as magnitude. Two different vectors are in use to represent a magnetic field: one called magnetic flux density, or magnetic induction, is symbolized by B; the other, called the magnetic field strength, or magnetic field intensity, is symbolized by H. The magnetic field H might be thought of as the magnetic field produced by the flow of current in wires and the magnetic field B as the total magnetic field including also the contribution made by the magnetic properties of the materials in the field. When a current flows in a wire wrapped on a soft-iron cylinder, the magnetizing field H is quite weak, but the actual average magnetic field (B) within the iron may be thousands of times stronger because B is greatly enhanced by the alignment of the iron's myriad tiny natural atomic magnets in the direction of the field. See also magnetic permeability.

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Universalium. 2010.

### Look at other dictionaries:

• Magnetic field — Field Field (f[=e]ld), n. [OE. feld, fild, AS. feld; akin to D. veld, G. feld, Sw. f[ a]lt, Dan. felt, Icel. fold field of grass, AS. folde earth, land, ground, OS. folda.] 1. Cleared land; land suitable for tillage or pasture; cultivated ground; …   The Collaborative International Dictionary of English

• magnetic field — n. (Physics) The space around a magnet through which it exerts magnetic force; a field of force surrounding a permanent magnet, electrical current, or a moving charged particle; called also {magnetic flux} and {field of magnetic force}. [WordNet… …   The Collaborative International Dictionary of English

• magnetic field — n the portion of space near a magnetic body or a current carrying body in which the magnetic forces due to the body or current can be detected <the magnetic field of the heart> * * * that portion of space about a magnet in which its action… …   Medical dictionary

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• magnetic Field —   [engl.], Magnetfeld …   Universal-Lexikon

• magnetic field — ► NOUN ▪ a region around a magnet within which the force of magnetism acts …   English terms dictionary

• Magnetic field — This article is about a scientific description of the magnetic influence of an electric current or magnetic material. For the physics of magnetic materials, see magnetism. For information about objects that create magnetic fields, see magnet. For …   Wikipedia

• magnetic field — noun the lines of force surrounding a permanent magnet or a moving charged particle (Freq. 3) • Syn: ↑magnetic flux, ↑flux • Hypernyms: ↑field, ↑field of force, ↑force field • Hyponyms …   Useful english dictionary

• magnetic field — UK / US noun [countable] Word forms magnetic field : singular magnetic field plural magnetic fields physics an area that the power of a magnet affects …   English dictionary