Important Magnetic Units, Terms, Symbols, and Formulas

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.

Flux (lines)ϕ
Weber (Wb)=number of lines 108 Weber (Wb)=number of lines 108
Flux density(magnetic flux per unit cross-sectional area at right angles to the flux lines)BB=ϕA=Tesla (T)B=ϕA=Tesla (T)
Magneto motive Force(that which forces magnetic lines of force through the magnetic circuit)MMFAmpere-Turn orAT=NIA−T=NI
Magnetic field intensity(magneto motive force per unit length)HNIlength=ATlengthNIlength=A−Tlength
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.μWebers per ampere-turn per meter 


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 (μo) is considered to be:


Relative Permeability(Not constant because it varies with the degree of magnetization)μrRelative permeability of a material is a ratio. Thus, 

μr=flux density with core material flux density with vacuum coreμr=flux density with core materialflux density with vaccum core


Where flux density in the core material is:

B=μoμrHB=μoμrH teslas,

and absolute permeability of core materials is:


Reluctance(Opposition to the establishment of magnetic flux)Ampere turns per Weber 


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