An expression for the electrostatic force between point charges: the force magnitude is proportional to the product of the charges and inversely proportional to the square of their separation, directed along the line joining them (vector form includes unit vector).

Principle

Inverse-square dependence and superposition: forces from multiple point charges add vectorially; the medium's permittivity scales the interaction strength.

Demonstration

A torsion-balance experiment measures the force between small charged spheres and shows the 1/r^2 dependence; in vacuum, the constant of proportionality is set by Coulomb's constant or the permittivity of free space.

Misapplication

Treating extended or continuous charge distributions as if they were single point charges without integration, ignoring dielectric screening, or applying it to rapidly moving charges where retardation and magnetic effects become significant.

Consequence

Forms the basis of electrostatics: defines the electric field of point charges, underlies Gauss's law in free space, and predicts forces and potentials between charges within its assumptions.

Reversal

Replacing Coulomb's instantaneous inverse-square law by full electrodynamics (retarded Liénard–Wiechert fields) or by screened potentials (e.g., Debye screening) in plasmas or electrolytes where simple 1/r^2 behaviour is modified.

Boundary

Valid for electrostatic interactions of point charges or symmetric distributions in linear, homogeneous, isotropic media at separations large compared to atomic scales; excludes time-varying fields, relativistic motion, quantum electrodynamic corrections, and environments with strong screening.

Semantic Tension

Tension between the simplicity of Coulomb's pairwise law and field- or quantum-based descriptions that treat interactions as mediated by fields or exchange particles — both predict forces but differ in causality, retardation, and many-body screening.

Synthesis

Coulomb's law is the classical inverse-square rule giving electrostatic force between charges in a given medium, accurate for static, pointlike or symmetric distributions but requiring electrodynamic or quantum corrections outside that regime.