Practice question

**Ferromagnetism** shows large positive χ ≈ 10³ to 10⁵, strong attraction, domain structure with spontaneous magnetization, hysteresis, retentivity. Distinction based on sign and magnitude of χ and behaviour in non-uniform field, explaining attraction versus repulsion. M = chi H . Given: chi = 9 × 10⁻⁴ , H = 2000 A m⁻¹ . M = 9 × 10⁻⁴ × 2000 = 1.8 A m⁻¹ . Substituting values gives 1.8 A m⁻¹, which matches expected magnitude for this magnetic configuration, confirming dipole field dependence on m/r³ and torque relation τ = m B sinθ.