Practice question

**Torque on magnetic dipole** in uniform field B is τ = m × B, magnitude τ = m B sinθ, m moment (A·m²), B field (T), θ angle between m and B (degrees). Torque tends to align moment with field, zero at θ = 0°, maximum mB at 90°, direction given by right-hand rule. B = μ₀ (H + M) , so H = (B/μ₀) - M . Given: B = 0.54 T , M = 4.0 × 10⁵ A m⁻¹ , μ₀ = 4π × 10⁻⁷ . (B/μ₀) = (0.54/4π × 10⁻⁷) ≈ 4.297 × 10⁵ A m⁻¹ . H = 4.297 × 10⁵