Practice question

**Line charge concept** extends point charge to infinite wire where symmetry dictates radial field proportional to λ and inversely proportional to distance r. λ = q/L for uniform case, field direction depends on sign of λ, outward for positive. Surface area: A = 4 π r² = 4 π (0.2)² = 0.16 π m² . Charge: q = sigma A = 30 × 10⁻⁶ × 0.16 π = 1.507 × 10⁻⁵ C . Substituting values gives 1.51 × 10⁻⁵ C, which matches expected magnitude for this electrostatic configuration, confirming Coulomb's and Gauss's principles and charge quantization consistency.