Problem 3.281

A permanent magnet is shaped as a ring with a narrow gap between the poles. The mean diameter of the ring equals \(d=20 \mathrm{~cm}\). The width of the gap is equal to \(b=2.0 \mathrm{~mm}\) and the magnetic induction in the gap is equal to \(B=40 \mathrm{mT}\). Assuming that the scattering of the magnetic flux at the gap edges is negligible, find the modulus of the magnetic field strength vector inside the magnet.