Coulomb's law defines the force, F, between charged particles q1 and q2 at a distance of 'r' in a vacuum as

F = k*(q₁q₂)/r², where k is a constant.

To measure the same forces in a non-vacuum, dielectric medium, such as the aqueous environment of biological systems, the dielectric constant () must be taken into account. The dielectric constant arises from the fact that the dielectric medium shields the charges from each other. This modifies Coulomb's law as follows:

F = k*(q₁q₂)/(*r²)

Thus, the larger the value of , the smaller the force between the charges.