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. Magnetic field B = (μ₀ N I/2 R) . B = (4 π × 10⁻⁷ × 45 × 1.2/2 × 0.06) = (21.6 π × 10⁻⁶/0.12) = 1.8 π × 10⁻⁴ ≈ 5.65 × 10⁻⁴ T . Using F = q v B sinθ, F = I l