Practice question

**Coulomb's law** gives force between point charges as F = k·|q₁q₂|/r², k = 1/(4π ε₀) = 9×10⁹ N·m²/C², directed along line joining charges. Like charges repel, opposite attract, magnitude scales with product of charges and inverse square of separation r². Insulators lack free charge carriers (e.g., electrons), preventing charge movement. Applied charges stay where they are placed due to the absence of conductivity, unlike conductors where charges redistribute freely. Substituting values gives Lack of free charges, which matches expected magnitude for this electrostatic configuration, confirming Coulomb's and Gauss's principles and charge quantization consistency.