Coulomb’s Law

Two stationary charges either attract or repel each other. The force of attraction or repulsion between them depends on their nature. Coulomb studied the nature of this force and in 1785 established a fundamental law governing it. From experimental observations, he showed that the electrical force between two static point charges q₁ and q₂ placed some distance apart is

• directly proportional to their product
• inversely proportional to the square of the distance r between them
• directed along the line joining the two charged particles
• repulsive for same kind of charges and attractive for opposite charges

ε₀ is called permittivity of free space. It means that if the same system of charges is kept in a material medium, the magnitude of Coulomb force will be different from that in free space.

ε₀ = 8.85 × 10^–12 C² N^–1 m^–2

k = 9 × 10⁹ N m² C^–2