Electrostatica

Electrostatics is the branch of physics that studies electric charges at rest and the electric fields and potentials they create. It is governed by Coulomb's law, which describes the force between stationary point charges: F = k q1 q2 / r^2, with k = 1/(4π ε0) in vacuum. The electric field due to a charge q is E = k q / r^2, and the electric potential V relates to the field by E = -∇V; the work done moving a test charge is qΔV. The superposition principle holds: the resultant field is the vector sum of individual fields.

Gauss's law provides a global relation between charge and field: ∮ E · dA = Q_enc / ε0. In media, Gauss's law is written with the displacement field D and permittivity ε. At electrostatic equilibrium, charges on conductors reside on surfaces and the field inside a conductor is zero; cavities can induce surface charges on the conductor.

Key concepts include capacitance C = Q/V, the energy stored in a capacitor as (1/2) C V^2, and the idea of shielding (Faraday cages) where external fields are attenuated by conductors. Dielectrics alter field strength via permittivity.

Applications of electrostatics span devices and processes: electronic device design, electrostatic painting and coating to control deposition, xerography and laser printing, electrostatic precipitators for air cleaning, and protection against electrostatic discharge in electronics manufacturing.

Classically, electrostatics is the static, low-frequency limit of electromagnetism; full Maxwell's equations describe both static and time-varying fields.