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 lines form closed loops because there are no magnetic monopoles, unlike electric field lines, which originate from positive charges and terminate at negative charges or extend to infinity. Using F = q v B sinθ, F = I l B sinθ, B = μ₀ I/(2π r),