Practice question

**Core magnetization** M = (μ_r -1)nI, so B = μ₀(nI + M). High μ_r materials like soft iron increase B dramatically for same nI, used in electromagnets, with μ_r up to 5000, enabling strong fields with low current. B = μ₀ μ_r n I , so I = (B/μ₀ μ_r n) . Given: B = 1.2 T , μ_r = 400 , n = 1500 m⁻¹ , μ₀ = 4π × 10⁻⁷ . I = (1.2/4π × 10⁻⁷ × 400 × 1500) = (1.2/7.539 × 10⁻¹) ≈ 1.592 A ≈ 1.6 A . Substituting values gives 1.6 A, which matches expected magnitude for this magnetic