In physics, the magnetomotive force (abbreviated mmf or MMF, symbol ) is a quantity appearing in the equation for the magnetic flux in a magnetic circuit, Hopkinson's law. It is the property of certain substances or phenomena that give rise to magnetic fields:
where Φ is the magnetic flux and is the reluctance of the circuit. It can be seen that the magnetomotive force plays a role in this equation analogous to the voltage V in Ohm's law, V = IR, since it is the cause of magnetic flux in a magnetic circuit:
where N is the number of turns in the coil and I is the electric current through the circuit.
where Φ is the magnetic flux and is the magnetic reluctance
where H is the magnetizing force (the strength of the magnetizing field) and L is the mean length of a solenoid or the circumference of a toroid.
The SI unit of mmf is the ampere, the same as the unit of current (analogously the units of emf and voltage are both the volt). Informally, and frequently, this unit is stated as the ampere-turn to avoid confusion with current. This was the unit name in the MKS system. Occasionally, the cgs system unit of the gilbert may also be encountered.
The term magnetomotive force was coined by Henry Augustus Rowland in 1880. Rowland intended this to indicate a direct analogy with electromotive force. The idea of a magnetic analogy to electromotive force can be found much earlier in the work of Michael Faraday (1791–1867) and it is hinted at by James Clerk Maxwell (1831–1879). However, Rowland coined the term and was the first to make explicit an Ohm's law for magnetic circuits in 1873.
Ohm's law for magnetic circuits is sometimes referred to as Hopkinson's law rather than Rowland's law as some authors attribute the law to John Hopkinson instead of Rowland. According to a review of magnetic circuit analysis methods this is an incorrect attribution originating from an 1885 paper by Hopkinson. Furthermore, Hopkinson actually cites Rowland's 1873 paper in this work.
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This course aims to teach essential notions of the structure of matter, chemical equilibria and reactivity. Classes and exercises provide the means to analyze and solve, by reasoning and calculation,
Un circuit magnétique est un circuit généralement réalisé en matériau ferromagnétique au travers duquel circule un flux de champ magnétique. Le champ magnétique est généralement créé soit par des enroulements enserrant le circuit magnétique et traversés par des courants, soit par des aimants contenus dans le circuit magnétique. Lorsque plusieurs circuits électriques sont bobinés autour d'un même circuit magnétique, ils constituent des circuits magnétiquement couplés. Il est constitué d'un assemblage de pièces en matériaux ferromagnétiques.
La réluctance, ou résistance magnétique, est une grandeur physique qui caractérise l'aptitude d'un circuit magnétique à s'opposer à sa pénétration par un champ magnétique. Le nom de cette grandeur a été créé par analogie avec celui de la résistance (électrique). L'inverse de la réluctance est appelé perméance magnétique. Cette analogie consiste à faire un parallèle entre les circuits électriques et les circuits magnétiques.
The MKS system of units is a physical system of measurement that uses the metre, kilogram, and second (MKS) as base units. The modern International System of Units (SI) was originally created as a formalization of the MKS system, and although the SI has been redefined several times since then and is now based entirely on fundamental physical constants, it still closely approximates the original MKS system for most practical purposes. By the mid-19th century, there was a demand by scientists to define a coherent system of units.
Couvre les courants des charges mobiles, la loi d'Ohm, les lois de Kirchhoff, et charge la conservation dans les circuits.
Explore le contexte historique de la distribution de l'énergie électrique et les concepts fondamentaux des courants et des circuits.
Couvre le modèle Drude pour les conductivités électriques et introduit les circuits DC.
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