Practice question

**Field at centre of circular loop** with N turns is B = μ₀ N I/(2R), R radius (m), direction along axis via right-hand rule, magnitude proportional to N I/R. For R = 0.09 m, N = 45, I = 1.2 A, B = 4π×10⁻⁷×45×1.2/(2×0.09) = 3.77×10⁻⁴ T, showing N enhancement. Torque tau = N I A B sin θ , where A = 0.25 × 0.25 = 0.0625 m² . tau = 20 × 2.5 × 0.0625 × 0.3 × sin 45° = 0.9375 × 0.707 = 0.6633 ≈ 0.66 N m . Using F = q v B sinθ, F = I l B