Coulomb's law states that the force of attraction or repulsion between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. Mathematically, it can be expressed as follows:

F = k * q1 * q2 / r^2

where:

* F is the force between the charges (in newtons)
* k is Coulomb's constant, which is equal to 8.9875 × 10^9 N m^2/C^2
* q1 and q2 are the magnitudes of the charges (in coulombs)
* r is the distance between the charges (in meters)

The force is attractive if the charges have opposite signs and repulsive if the charges have the same sign.

In the case of dielectrics, the presence of the dielectric material reduces the force between the charges. This is because the dielectric material polarizes, meaning that it aligns its own electric charges in response to the external charges. The dielectric constant of a material is a measure of how much it reduces the force between charges. The higher the dielectric constant, the greater the reduction in force.

The unit of charge, the coulomb, is defined as the amount of charge that must be placed on a small sphere in a vacuum so that it experiences a force of 1 newton when placed 1 meter away from another small sphere with a charge of the same magnitude.

Here are some examples of Coulomb's law in action:

* Two positive charges will repel each other.
* Two negative charges will repel each other.
* A positive charge and a negative charge will attract each other.
* A charge placed near a dielectric material will experience a weaker force than it would if it were placed in a vacuum.