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. μ_r = 1 + chi . Given: chi = -4 × 10⁻⁵ . Substitute: μ_r = 1 - 4 × 10⁻⁵ = 0.99996 . Substituting values gives 0.99996, which matches expected magnitude for this magnetic configuration, confirming dipole field dependence on m/r³ and torque relation τ = m B sinθ.