Find the electrostatic force between two point charges with F = k q₁ q₂ / r² — or solve for a charge or the separation. Uses Coulomb's constant k = 8.988×10⁹ N·m²/C².
Coulomb's law gives the force between two point charges: F = k q₁ q₂ / r², where k = 8.988×10⁹ N·m²/C², charges are in coulombs and separation in metres. Like Newton's gravity, it follows an inverse-square law.
If both charges have the same sign the force is repulsive (positive); opposite signs give an attractive (negative) force. When solving for a charge or distance this calculator uses the magnitudes; interpret the sign from whether the charges are alike or opposite.
Coulomb's law states the electric force between two point charges is F = k q₁q₂/r² — proportional to the product of the charges and inversely proportional to the square of the distance between them.
k ≈ 8.988×10⁹ N·m²/C², often rounded to 9×10⁹. It equals 1/(4πε₀), where ε₀ is the permittivity of free space.
Like charges (both + or both −) repel; opposite charges attract. The sign of the product q₁q₂ tells you: positive means repulsion, negative means attraction.
Both are inverse-square laws with the same 1/r² form. Coulomb's law can be attractive or repulsive, while gravity is always attractive and vastly weaker.