Coulomb's Law describes the interaction between point electric charges.
It was discovered by Charles-Augustin de Coulomb in 1785. After conducting numerous experiments with metallic spheres, Coulomb formulated the law as follows:
The force of interaction between two stationary point charges in a vacuum is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them.
It is important to note that for the law to hold, the following conditions must be met:
- The charges must be point-like — meaning the distance between the charged bodies is much greater than their dimensions.
- The charges must be stationary; otherwise, the magnetic field produced by moving charges must also be taken into account.
where F⃗12 is the force exerted by charge 1 on charge 2; q1, q2 are the magnitudes of the charges; r⃗12 is the radius vector (directed from charge 1 to charge 2 and equal in magnitude to the distance between the charges — r12); k is the proportionality constant.
Coefficient k
In the CGSE system, the unit of charge is chosen so that k = 1, and it is usually omitted.
In the SI system, k ≈ 8.987742438·109 N·m2/C2 (or F-1·m) and is expressed as follows:
where ≈ 8.854187817·10−12 F/m is the electric constant (vacuum permittivity).
In a homogeneous isotropic medium, the dielectric permittivity ε of the medium is introduced into the denominator of the formula.
In SI units:
