Practice question

**SI unit of magnetic field** is tesla (T), defined as force 1 N on 1 A·m wire perpendicular to field. Moving coil galvanometer uses torque τ = N I A B balanced by spring torque k φ, so deflection φ ∝ I, enabling current measurement, with radial field ensuring τ = N I A B always maximum. B = (μ₀ I/2 π r) , so r = (μ₀ I/2 π B) . r = (4 π × 10⁻⁷ × 14/2 π × 7 × 10⁻⁶) = (56 × 10⁻⁷/14 × 10⁻⁶) = 0.4 m . Using F = q v B sinθ, F = I