# 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) B B=ϕA=Tesla (T)B=ϕA=Tesla (T) Magneto motive Force(that which forces magnetic lines of force through the magnetic circuit) MMF Ampere-Turn orA−T=NIA−T=NI Magnetic field intensity(magneto motive force per unit length) H NIlength=A−TlengthNIlength=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. μ Webers per ampere-turn per meter μ=lRAμ=lℜAwhere length (l) is length in meters reluctance (ℜ) is ampere-turns per weberarea (A) is cross-sectional area in square metersNote: Free space, or vacuum permeability (μo) is considered to be:4π×10-7 Relative Permeability(Not constant because it varies with the degree of magnetization) μr Relative 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:μ=BH=μoμrμ=BH=μoμr Reluctance(Opposition to the establishment of magnetic flux) ℜ Ampere turns per Weber R=MMFϕ=A−TWb

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