Problem 3.282

An iron core shaped as a tore with mean radius $R=250 \mathrm{~mm}$ supports a winding with the total number of turns $N=1000$. The core has a cross-cut of width $b=1.00 \mathrm{~mm} .$ With a current $I=$ $=0.85$ A flowing through the winding, the magnetic induction in the gap is equal to $B=0.75 \mathrm{~T}$. Assuming the scattering of the magnetic flux at the gap edges to be negligible, find the permeability of iron under these conditions.