We know that two like or similar charges repel each other and two opposite charges attract each other ( To know more about electric charge click here... ). In 1785 French physicist

**determined the magnitude of this attraction and repulsion force and published a law about it. This law is known as***Charles Augustin de Coulomb***. Here we will discuss this law***Coulomb's Law***What is Coulomb's Law?**

According to

**the effective force of attraction or repulsion between two stationary point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.***Coulomb’s law,*This force acts along the connecting line of the two charges and its value depends on the nature of the medium in which the charges are located.

**Coulomb's formula:**Consider, two points charges

*q1*and

*q2*, are at a distance of

*r*from each other. If the magnitude of the force is

*F*, then according to Coulomb's law

Here k is a constant known as the electrostatic force constant or coulomb constant. It depends on the units of

*F, r*,*q1*,*q2*, and on the nature of the medium in which the charges are located.**Coulomb's law in SI unit system**

If the two charges are in a vacuum, then in the SI unit system

*k = 1/4𝜋𝜀o*. Where*𝜀o*is the*permittivity of free-space/vacuum*.Now if the two charges are in the real medium, then

*k = 1/4𝜋𝜀*. Where*𝜀*is the*.***permittivity of that medium**So in the SI unit system the Coulomb's law written as

**Coulomb's law in CGS unit system**

In the CGS unit system

*k = 1/K*, Where*K*is the*of the medium. So in the CGS unit system the Coulomb's law written as***dielectric constant**If the medium is taken as a vacuum then K = 1, so the law can be written as

**Read next:**What is the Permittivity of Free Space?