MAGNETISM Basic Electrical TheoryGenerally, different types of materials have different values of reluctance (Figure 25). Air gapis the air space between two poles of a magnet. Since air has a very high reluctance, the sizeof the air gap affects the value of reluctance: the shorter the air gap, the stronger the field in thegap. Air is nonmagnetic and will not concentrate magnetic lines. The larger air gap onlyprovides space for the magnetic lines to spread out.SummaryThe important information contained in this chapter is summarized below.Magnetism SummaryMagnetic flux - group of magnetic field lines that are emitted outward from thenorth pole of a magnetMagnetic flux density - amount of magnetic flux per unit area of a section,perpendicular to the direction of the fluxWeber - measure of magnetic fluxPermeability - ability of a material to concentrate magnetic lines of fluxFerromagnetic materials - iron, steel, nickel, cobalt, and commercial alloys withrelative permeability ranging from 50-200Paramagnetic materials - aluminum, platinum, manganese, and chromium withrelative permeability of slightly more than oneDiamagnetic materials - bismuth, antimony, copper, zinc, mercury, gold, andsilver with relative permeability of less than oneMagnetomotive force (mmf) - strength of a magnetic field in a coil of wiredependent on current flowing through coilAmpere turns - current flowing through a coil times the number of turns in thecoilField intensity - identifies the magnetic flux density per unit length of a coilReluctance - opposition to the production of flux in a materialES-01 Page 36 Rev. 0
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