Physics
With a material between the charges
A dielectric reduces the force by its relative permittivity.
The Formula
F = k x |q1| x |q2| / (relative permittivity x r^2)
A dielectric reduces the force by its relative permittivity.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| relative permittivity | Dielectric constant | unitless | One in a vacuum, about 78 in water. |
| F | Force | newtons | The force in the medium. |
| r | Separation | metres | The distance between the charges, in metres. |
What Each Symbol Means
relative permittivityunitless
Dielectric constant
One in a vacuum, about 78 in water.
Fnewtons
Force
The force in the medium.
rmetres
Separation
The distance between the charges, in metres.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate coulomb's law page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Coulomb's Law, filed under Science. Every number the guide produces comes from substituting into this one line.