Coulomb's Law
Discussion
Introduction
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 = k | q1q2 |
| r2 |
where…
| F = | magnitude of the electrostatic force |
| ke = | electrostatic constant = 8.99 × 109 N m2/C2 |
| q1, q2 = | charges of the two objects |
| r = | separation between the charges |
or…
| F = | 1 | q1q2 | r̂ | |
| 4πε0 | r2 |
where…
| F = | electrostatic force vector |
| ε0 = | vacuum permittivity = 8.8541878128 × 10−12 C2/N m2 |
| q1, q2 = | charges of the two objects |
| r = | separation between the charges |
| r̂ = | unit vector in the radial direction |
text
- 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.