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Coulomb's law quantifies the electrostatic force between two stationary point charges. The force F = kq1q2/r^2, where k = 1/(4piepsilon_0) = 9 x 10^9 N m^2 C^(-2), q1 and q2 are the charges, and r is the separation. The force is attractive for opposite charges and repulsive for like charges, acting along the line joining them.

In a dielectric medium with constant K (relative permittivity), the force is reduced: F_medium = F_vacuum/K. This is because the medium partially screens the charges through polarization. The permittivity of free space epsilon_0 = 8.854 x 10^(-12) C^2 N^(-1) m^(-2) with dimensions [M^(-1) L^(-3) T^4 A^2].

The principle of superposition states that the net force on any charge equals the vector sum of individual Coulomb forces from all other charges. Each pairwise interaction is independent — no three-body corrections exist. For symmetric charge configurations (equilateral triangle, square), exploit symmetry to simplify vector addition.

Key quantitative results for JEE: the force between two 1 C charges at 1 m is 9 x 10^9 N (enormous), showing that everyday charges are in micro- or nanocoulombs. The electrostatic force is ~10^39 times stronger than gravity between an electron and proton. When a charge Q is split into q and (Q-q), the mutual repulsion is maximized when q = Q/2 (by AM-GM inequality).

Coulomb's law parallels Newton's gravitational law but differs in being both attractive and repulsive, medium-dependent, and enormously stronger. Both obey the inverse-square law and superposition.