Practice question

**Elements of Earth's field** include declination D, inclination I, horizontal component B_H, total field B = √(B_H² + B_V²). B_H provides compass direction, declination varies with location, important for navigation, inclination 0° at magnetic equator, 90° at poles. B = μ₀ (H + M) , so M = (B/μ₀) - H . Given: B = 0.55 T , H = 3500 A m⁻¹ , μ₀ = 4π × 10⁻⁷ . (B/μ₀) = (0.55/4π × 10⁻⁷) ≈ 4.375 × 10⁵ A m⁻¹ . M = 4.375 × 10⁵ - 3500 ≈ 4.34 × 10⁵ A m⁻¹ . Substituting values gives 4.34 × 10⁵ A m⁻¹, which