magnetism - Charged particle in a magnetic field, Magnetic dipoles, Magnetic monopoles, Atomic magnetic dipoles, Units of electromagnetism

Phenomena associated with magnetic fields and magnetic materials, and the study of such phenomena. All magnetic effects ultimately stem from moving electric charges, and all materials have magnetic properties. Electric coils, currents in wires, and permanent magnets are all sources of magnetic field.

Electromagnetism
Magnetism
Electrostatics
Electric charge
Coulomb's law
Electric field
Gauss's law
Electric potential
Magnetostatics
Ampere's law
Magnetic field
Magnetic moment
Electrodynamics
Electric current
Lorentz force law
Electromotive force
Electromagnetic induction
Faraday-Lenz law
Displacement current
Maxwell's equations
Electromagnetic field
Electromagnetic radiation
Electrical circuits
Electrical conduction
Electrical resistance
Capacitance
Inductance
Impedance
Resonant cavities
Waveguides
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In physics, magnetism is one of the phenomena by which materials exert an attractive or repulsive force on other materials.

Charged particle in a magnetic field

When a charged particle moves through a magnetic field B, it feels a force F given by the cross product:

where is the electric charge of the particle is the velocity vector of the particle is the magnetic field.

Magnetic dipoles

Normally, magnetic fields are seen as dipoles, having a "South pole" and a "North pole"; Therefore, when placed in a magnetic field, a magnetic dipole tends to align itself in opposed polarity to that field, thereby canceling the net field strength as much as possible and lowering the energy stored in that field to a minimum.

Magnetic monopoles

The modern understanding of magnetism posits that all magnetic effects are actually due to the motion of charged particles;

Since all known forms of magnetic phenomena involve the motion of electrically charged particles, and since no theory suggests that "pole" is, in that context, a thing rather than a convenient fiction, it may well be that nothing that could be called a magnetic monopole exists or ever did or could.

Atomic magnetic dipoles

The physical cause of the magnetism of objects, as distinct from electrical currents, is the atomic magnetic dipole. Magnetic dipoles, or magnetic moments, result on the atomic scale from the two kinds of movement of electrons. The second, much stronger, source of electronic magnetic moment is due to a quantum mechanical property called the spin dipole magnetic moment (although current quantum mechanical theory states that electrons neither physically spin, nor orbit the nucleus).

The overall magnetic moment of the atom is the net sum of all of the magnetic moments of the individual electrons. Because of the tendency of magnetic dipoles to oppose each other to reduce the net energy, in an atom the opposing magnetic moments of some pairs of electrons cancel each other, both in orbital motion and in spin magnetic moments. Thus, in the case of an atom with a completely filled electron shell or subshell, the magnetic moments normally completely cancel each other out and only atoms with partially-filled electron shells have a magnetic moment, whose strength depends on the number of unpaired electrons.

The differences in configuration of the electrons in various elements thus determine the nature and magnitude of the atomic magnetic moments, which in turn determine the differing magnetic properties of various materials. Several forms of magnetic behavior have been observed in different materials, including:

Diamagnetism Paramagnetism Molecular magnet Ferromagnetism Antiferromagnetism Ferrimagnetism Metamagnetism Spin glass Superparamagnetism

Magnetars, stars with extremely powerful magnetic fields, are also known to exist. The physical and magnetic properties of the product depend on the raw materials, but are generally lower in magnetic strength and resemble plastics in their physical properties.

Rare earth magnets

'Rare earth' (lanthanoid) elements have a partially occupied f electron shell (which can accommodate up to 14 electrons.) The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore these elements are used in compact high-strength magnets where their higher price is not a factor.

Neodymium iron boron (NIB)

Neodymium magnets, more formally referred to as neodymium iron boron (NdFeB) magnets, have the highest magnetic field strength, but are inferior to samarium cobalt in resistance to oxidation and temperature.

See results from NIST published April 2005, or

Units of electromagnetism

SI magnetism units

edit SI electromagnetism units
Symbol	Name of Quantity	Derived Units	Unit	Base Units
I	Magnitude of current	ampere (SI base unit)	A	A = W/V = C/s
q	Electric charge, Quantity of electricity	coulomb	C	A·s
V	Potential difference or Electromotive force	volt	V	J/C = kg·m·A−1
R, Z, X	Resistance, Impedance, Reactance	ohm	Ω	V/A = kg·m·A−2
ρ	Resistivity	ohm metre	Ω·m	kg·m·A−2
P	Power, Electrical	watt	W	V·A = kg·m
C	Capacitance	farad	F	C/V = kg·A
	Elastance	reciprocal farad	F−1	V/C = kg·m·s−4
ε	Permittivity	farad per metre	F/m	kg·A
χe	Electric susceptibility	(dimensionless)	-	-
G, Y, B	Conductance, Admittance, Susceptance	siemens	S	Ω·m·A2
σ	Conductivity	siemens per metre	S/m	kg·s
H	Magnetic field, magnetic field intensity	ampere per metre	A/m	A·m−1
Φm	Magnetic flux	weber	Wb	V·s = kg·m·A−1
B	Magnetic flux density, magnetic induction, magnetic field strength	tesla	T	Wb/m·A−1
	Reluctance	ampere-turn per weber	A/Wb	kg·s
L	Inductance	henry	H	Wb/A = V·s/A = kg·m·A−2
μ	Permeability	henry per metre	H/m	kg·m·s
χm	Magnetic susceptibility	(dimensionless)	-	-

Other magnetism units

gauss-The gauss, abbreviated as G, is the cgs unit of magnetic flux density or magnetic induction (B).