Coulombtörvény

Coulombtörvény, or Coulomb's law, is a fundamental principle of electrostatics that describes the force between stationary point charges. It states that the magnitude of the electrostatic force between two point charges q1 and q2 separated by distance r is F = ke |q1 q2| / r^2, where ke is Coulomb's constant, approximately 8.9875 × 10^9 N·m^2/C^2. The force is along the line connecting the charges and is attractive for opposite signs and repulsive for like signs.

Vector form: the force on charge 1 due to charge 2 is F⃗ = ke q1 q2 r⃗12 / r^3, where r⃗12 points from charge 1 to charge 2 and r = |r⃗12|.

In a dielectric medium with permittivity ε = ε0 εr, the law becomes F = (1 / (4π ε)) q1 q2 / r^2, and ke is replaced by 1/(4π ε). Thus the medium reduces the effective force by the relative permittivity εr.

Coulomb's law is the electrostatic limit of Maxwell's equations for stationary charges. When charges move, magnetic effects and the finite speed of propagation must be accounted for; the general description is provided by classical electrodynamics (e.g., Liénard–Wiechert potentials).

History and scope: the law was formulated by Charles-Augustin de Coulomb in the 1780s using a torsion balance. It applies to point charges and is a good approximation at low speeds and moderate distances; at very short distances or high field strengths quantum or relativistic effects may be relevant.

Applications include calculating electric forces, designing capacitors, and understanding atomic and molecular interactions. Units are newtons for force, coulombs for charge, and meters for distance.