Practice question

**Potential energy of magnetic dipole** U = -m B cosθ explains stability. Given m = 0.9 A·m², B = 0.5 T, θ = 90°, sin90° = 1, τ = 0.45 N·m. For 60°, sin60° = √3/2 ≈0.866, reducing torque proportionally. B = μ₀ (H + M) , so H = (B/μ₀) - M . Given: B = 0.3 T , M = 1.5 × 10⁵ A m⁻¹ , μ₀ = 4π × 10⁻⁷ . (B/μ₀) = (0.3/4π × 10⁻⁷) ≈ 2.387 × 10⁵ A m⁻¹ . H = 2.387 × 10⁵ - 1.5 × 10⁵ = 8.87 × 10⁴ A m⁻¹ ≈ 8.9 × 10⁴