The transformer in Figure 10.13b consists of a core with relatively high reluctance (low permeability); therefore, the
approximation of infinite permeability cannot be used. If we wish to calculate the ratio between primary and secondary, we
must calculate the flux in the magnetic circuit. We first assume that all flux links both coils of the transformer (no flux
leakage), but permeability is finite. The net flux in the magnetic circuit linking both coils in Figure 10.13b is