Coulomb's law


Coulomb's law is a fundamental principle in electrostatics that describes the force of attraction or repulsion between two point charges. It states that the force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. The force is also attractive between charges of opposite sign and repulsive between charges of the same sign.

  • ·         F is the magnitude of the electrostatic force (in Newtons, N)
  • ·         k is Coulomb's constant (8.988 ×109 N.m2C2)
  • ·         q1 and q2 are the magnitudes of the two charges (in Coulombs, C)
  • ·         d is the distance between the two charges (in meters,)

Direction of the Force

The force is directed along the line connecting the two charges. If the charges have the same sign (both positive and negative), the force is repulsive. If the charges have the opposite sign, the force is attractive.


·         A positively charged balloon will attract a negatively charged piece of paper.

·         Two positively charged ions will repel each other.

·         Two negatively charged electrons will repel each other.

Limitations of Coulomb's Law

Coulomb's law only applies to point charges. This means that the charges are considered to be infinitely small and have no spatial extent. In reality, all charges have a finite size, and this can affect the force between them.

Coulomb's law also only applies to static charges. This means that the charges are not moving. If the charges are moving, then they will also experience a magnetic force, in addition to the electrostatic force.

Applications of Coulomb's Law

Coulomb's law is a fundamental law of physics that has a wide range of applications. Some of these applications include:

·         The behavior of electrons in atoms and molecules

·         The behavior of electric circuits

·         The operation of electrostatic precipitators, which are used to remove pollutants from smokestacks

·         The operation of electric motors and generators

·         The operation of batteries

Formulas and Constants




Coulomb's constant


8.988 × 109 N·m2/C2

Vacuum permittivity


8.854 × 10−12 C²/N·m²

Electron charge


-1.602 × 10−19 C

Proton charge


+1.602 × 10−19 C

Atomic unit of charge


+1.602 × 10−19 C