Practice question

**Hysteresis loop** plots B versus H for ferromagnetic material, retentivity (remanence) is residual B at H=0 after saturation, coercivity is reverse H needed to reduce B to zero. Hard ferromagnets have high retentivity and coercivity, retaining strong magnetism after external field removed, suitable for permanent magnets. B = μ₀ (H + M) , so M = (B/μ₀) - H . Given: B = 0.48 T , H = 3200 A m⁻¹ , μ₀ = 4π × 10⁻⁷ . (B/μ₀) = (0.48/4π × 10⁻⁷) ≈ 3.819 × 10⁵ A m⁻¹ . M = 3.819 × 10⁵ - 3200 ≈ 3.787 × 10⁵ A m⁻¹ . Substituting