Practice question

**Solenoid with magnetic core** produces field B = μ₀ μ_r n I inside, μ₀ = 4π×10⁻⁷ T·m/A, μ_r relative permeability, n = N/L turns per meter, I current. Core enhances field μ_r times, so given B, μ_r, n, current I = B/(μ₀ μ_r n) can be found, illustrating core effect on field strength. B = μ₀ μ_r n I , so I = (B/μ₀ μ_r n) . Given: B = 0.8 T , μ_r = 400 , n = 800 m⁻¹ , μ₀ = 4π × 10⁻⁷ . Substitute: I = (0.8/4π × 10⁻⁷ × 400 × 800) = (0.8/4π × 3.2 × 10⁻²) ≈