Practice question

**Geomagnetic field** arises from outer core dynamo, field lines emerge near geographic south pole. Understanding D and I allows conversion between geographic and magnetic coordinates, with B_H = B cos(inclination) used in experiments with tangent galvanometer. B = μ₀ (H + M) , so M = (B/μ₀) - H . Given: B = 0.2 T , H = 1000 A m⁻¹ , μ₀ = 4π × 10⁻⁷ . (B/μ₀) = (0.2/4π × 10⁻⁷) ≈ 1.59 × 10⁵ A m⁻¹ . M = 1.59 × 10⁵ - 1000 = 1.58 × 10⁵ A m⁻¹ . Substituting values gives 1.58 × 10⁵ A m⁻¹, which matches expected