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. tau = m B sinθ . Given: m = 0.35 A m² , B = 0.9 T , θ = 30° , sin 30° = 0.5 . tau = 0.35 × 0.9 × 0.5 = 0.1575 N m . Substituting values gives 0.1575 N m, which matches expected magnitude for this magnetic configuration, confirming dipole field dependence on m/r³ and torque relation τ = m B sinθ.