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. In diamagnetic materials, an external magnetic field induces orbital currents in atoms that oppose the applied field, per Lenz’s law. This results in a weak, negative magnetization, as all electrons contribute to this effect in materials with no net magnetic moment. Substituting values gives Induced currents opposing the field, which matches expected