magnet formulas
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Maxwell’s Equations
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Wherever you go. Whatever you do. Make sure you don’t try to build
something that doesn’t agree with these little gems.
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I
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Gauss's Law for Electricity. The surface integral of electric field
over any closed surface is proportional to the enclosed charge. The k
factor is the dielectric constant, equal to 1 in free space.
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II
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Gauss's Law for Magnetism. The integral of magnetic flux density over
any closed surface is zero. This is the mathematical expression of the
fact that no magnetic monopoles have ever been discovered.
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III
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Faraday's Law of Induction. The line integral of electric field over
any closed path is proportional to the rate of change of magnetic flux
in the enclosed region.
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IV
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Ampere's Law (as extended by Maxwell). The line integral of magnetic
flux density over any closed path is proportional to the rate of change
of electric field and electric current in the enclosed region. The κ
m factor is the relative permeability, equal to 1 in free space.
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Those Little Constants
All of the preceding equations work with units of meters, seconds, teslas
(units of induced magnetic flux density, commonly referred to as "magnetic
field" or "field"), webers (units of induced magnetic flux), amperes,
volts and coulombs. The constants have the following values:
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εo
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8.85 x 10-12 F/m
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Permittivity constant
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μo
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1.26 x 10-6 H/m
(exactly 4π x 10-7)
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Permeability constant
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