The force between two point charges is …
- directly proportional to the magnitude of each charge (q1, q2),
- inversely proportional to square of the separation between their centers (r),
- directed along the separation vector connecting their centers (r̂).
This relationship is known as Coulomb's Law. Charles-Augustin Coulomb (1736–1806) France. As an equation it is usually written in one of two forms …
|F = ||ke ||q1q2 || r̂ || ||or ||F = ||1 || ||q1q2 || r̂ || |
|r2 ||4πε0 ||r2 |
| || || |
|ke = ||electrostatic constant |
8.99 × 109 Nm2/C2
| ||ε0 = ||vacuum permittivity |
8.85 × 10−12 C2/Nm2
- When two charges have the same sign
their product is positive,
which means the force vector is directed with the separation vector (r̂)
and the action is repulsive.
- When two charges have the opposite sign
their product is negative,
which means the force vector is directed against the separation vector (r̂)
and the action is attractive.