- is Coulomb's law for the force between two charged particles separated by a distance r: ke≈8.987×109N·m²·C−2, and ε0≈8.854×10−12 F·m−1.
- is the electric force on a "test charge", q, where is the magnitude of the electric field situated a distance r from a charge, Q.
Consider a collection of particles of charge , located at points (called source points), the electric field at (called the field point) is:
- is the electric field at the field point, , due to point charges at the source points, , and points from source points to the field point.
is the electric field due to distributed charge, where , and denote linear, surface, and volume density (or charge density), respectively.
Cartesian coordinates (x, y, z). Volume element: . Line element:. Three basic area elements: , or,, or,.
Cylindrical coordinates (ρ, φ, z): Volume element: . Line element:. Basic area elements: (side), and, (top end).
Spherical coordinates (r, θ, φ): Volume element: (if symmetry holds). Line element:. Basic area element of a sphere: , where dΩ is a solid angle.