The following table presents important Magnetic Units, Symbols, and Their Formulas as a reference, or source of information. These formulas play a key role while dealing with magnetic circuits such as Transformers, Inductors.
Term or quantity | Symbol or abbreviation | SI Unit and Formula |
Flux (lines) | ϕ | \[Weber\text{ }\left( Wb \right)=\frac{number\text{ }of\text{ }lines}{{{10}^{8}}}\] |
Flux density
(magnetic flux per unit cross-sectional area at right angles to the flux lines) |
B | $B=\frac{\phi }{A}=Tesla\text{ }(T)$ |
Magneto motive Force
(that which forces magnetic lines of force through the magnetic circuit) |
MMF | Ampere-Turn or
$A-T=NI$ |
Magnetic field intensity
(magneto motive force per unit length) |
H | $\frac{NI}{length}=\frac{A-T}{length}$ |
Permeability
(Ability of a material to pass, conduct, or concentrate magnetic flux; analogous to conductance in electrical circuits), i.e., the ease of establishing magnetic flux through the material. |
μ | Webers per ampere-turn per meter
$\mu =\frac{l}{\Re A}$ where length (l) is length in meters reluctance (ℜ) is ampere-turns per weber area (A) is cross-sectional area in square meters Note: Free space, or vacuum permeability (μ_{o}) is considered to be: 4π×10^{-7} |
Relative Permeability
(Not constant because it varies with the degree of magnetization) |
μ_{r} | Relative permeability of a material is a ratio. Thus,
${{\mu }_{r}}=\frac{flux\text{ }density\text{ }with\text{ }core\text{ }material}{flux\text{ }density\text{ }with\text{ }vaccum\text{ }core}$
Where flux density in the core material is: $B={{\mu }_{o}}{{\mu }_{r}}H$ teslas, and absolute permeability of core materials is: $\mu =\frac{B}{H}={{\mu }_{o}}{{\mu }_{r}}$ |
Reluctance
(Opposition to the establishment of magnetic flux) |
ℜ | Ampere turns per Weber
$\Re =\frac{MMF}{\phi }=\frac{A-T}{Wb}$ |