Practice question

**Independent action of charges** allows total force or field as vector sum. Geometry dictates distances to evaluation point, and resultant follows Σ k q_i/r_i², explaining zero field at symmetric centres for equal charges. E = (k q/r²) . 6 × 10³ = 9 × 10⁹ × (q/(0.24)²) . q = (6 × 10³ × 0.0576/9 × 10⁹) = 3.84 × 10⁻⁸ C . Substituting values gives 3.84 × 10⁻⁸ C, which matches expected magnitude for this electrostatic configuration, confirming Coulomb's and Gauss's principles and charge quantization consistency.