Practice question

**Electric field concept** visualizes influence of source charge. Uniform field exerts constant force F = qE, and flux Φ = E·A = E A cosθ links field to area orientation, maximum when field normal to surface. E = (k q/r²) . 5 × 10³ = 9 × 10⁹ × (q/(0.4)²) . q = (5 × 10³ × 0.16/9 × 10⁹) = 8.89 × 10⁻⁸ C . Substituting values gives 8.89 × 10⁻⁸ C, which matches expected magnitude for this electrostatic configuration, confirming Coulomb's and Gauss's principles and charge quantization consistency.