The law stating that electric force is proportional to the product of two charges and inversely proportional to the square of their separation is Coulomb’s law.
For point charges, its magnitude is written F = kₑ|q₁q₂|/r². Here, q₁ and q₂ are the charges, r is their distance apart, and kₑ is the Coulomb constant. Like charges repel, while opposite charges attract; the force acts along the straight line joining them.
French physicist Charles-Augustin de Coulomb published the law in 1785 after experiments using a torsion balance. The inverse-square relationship resembles Newton’s law of universal gravitation, but gravity is always attractive, whereas electric forces can attract or repel. Electric forces are also vastly stronger at the scale of individual particles.
Coulomb’s law applies most directly to stationary point charges or spherically symmetric charge distributions. Moving charges can produce magnetic effects, so a complete description then requires Maxwell’s equations. The law also underlies the definition of the electric field and helps explain atomic and ionic forces.