Practice question

**Biot-Savart law** dB = μ₀/4π·I dl × r̂/r² underlies both straight wire and loop formulas. For square loop side a, area A = a², moment m = N I A, field pattern similar to dipole at large distances, with superposition for N turns. Torque tau = N I A B sin θ , where A = 0.12 × 0.12 = 0.0144 m² . tau = 35 × 1.8 × 0.0144 × 0.5 × sin 30° = 0.9072 × 0.5 = 0.4536 ≈ 0.45 N m . Using F = q v B sinθ, F = I l B sinθ, B = μ₀ I/(2π r), B