Inductors discussed in Chap. 6 mostly have one winding only and a relatively large air gap to make it a linear device, where current and voltage are proportional to each other: if one defines in the time domain 7.1a $$ {{\hbox{v}}_{\rm{L}}}({\hbox{t}}) = {\hbox{L}}\frac{{{\text{d}}{{\text{i}}_{\rm{L}}}{\text{(t)}}}}{\hbox{dt}}, $$ then one can write in the phasor domain 7.1b $$ \tilde{\rm v}_{\rm{L}}(\hbox{t}) = {\rm j}\omega {\rm L}{\tilde{\rm i}}_{\rm{L}}(\hbox{t}), $$ where the inductance L is constant.