Practice question

**Magnetic properties** μ_r = 400 indicates 400 times vacuum permeability, so B enhanced 400 times for same nI. H = nI (A/m) for solenoid, M = χ H, B = μ₀(H+M) links microscopic magnetization to macroscopic field. In ferromagnetic materials, the magnetic field inside increases significantly because the external field aligns and expands pre-existing magnetic domains, enhancing the overall magnetization and field strength far beyond the applied field. Substituting values gives Alignment and growth of magnetic domains, which matches expected magnitude for this magnetic configuration, confirming dipole field dependence on m/r³ and torque relation τ = m B sinθ.