Define a unit charge.

A unit charge refers to a charge of one coulomb which is the standard unit of charge. One Coulomb of charge is equal to electrons or protons. One electron is equal to Coulombs. It is defined as the charge transported by a steady current of one ampere in one second.
⇒ 1C = 1A × 1S

From Coulomb’s Law, we know that the electrostatic force of attraction or repulsion between two charges is directly proportional to the product of the two charges and is inversely proportional to the square of the distance between the charges. So, it can be written as,

F ∝ q1q2/r2

F = 1/4πε x q1q2/r2

  • q1 and q2 are the two charges.
  • r is the distance between the two charges.
  • ε is absolute permittivity,

A coulomb is that charge which repels an equal charge of the same sign with a force of 9×109 N, when the charges are one meter apart in a vacuum. Coulomb force is the conservative mutual and internal force.

The value of εo is 8.86 × 10-12 C2/Nm2 (or) 8.86 × 10-12 Fm–1

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