Coulomb’s Law

Formula

Description

Coulomb’s law gives the electrostatic force between two point charges. The force is proportional to the product of the charges and falls off with the square of the distance between them, exactly analogous to gravity. Like charges repel and unlike charges attract. It is the foundation of electrostatics and underlies capacitance, dielectric behaviour, and the forces in every electronic material.

Variables

• F — Electrostatic force (N)
• q1, q2 — The two point charges (C)
• r — Separation between charges (m)
• kₑ — Coulomb constant 8.988×10⁹ N·m²/C²

Practical Notes

The Coulomb constant kₑ = 1/(4πε₀). The inverse-square dependence means halving the distance quadruples the force. In a dielectric medium the force is reduced by the relative permittivity εr.