Practice question

**Electrostatic force** described by F = (1/4π ε₀)·q₁q₂/r² obeys Newton's third law. Magnitude depends on q₁q₂ and 1/r², enabling quantitative estimation at given separation, with sign indicating attraction or repulsion. Negative charge means electrons gained. q = n e , e = -1.6 × 10⁻¹⁹ C . n = (q/|e|) = (1.28 × 10⁻⁷/1.6 × 10⁻¹⁹) = 8 × 10¹¹ . Substituting values gives 8 × 10¹¹, which matches expected magnitude for this electrostatic configuration, confirming Coulomb's and Gauss's principles and charge quantization consistency.