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. tau = N I A B sin θ , where θ = 30° to plane means sin 60° with normal. tau = 15 × 2.5 × 0.08 × 0.6 × sin 30° = 1.8 × 0.5 = 0.9 N m . Using F = q v B sinθ, F = I l B sinθ, B = μ₀ I/(2π r), B = μ₀