Elektrostat

Elektrostat, or electrostatics, is the branch of physics that studies electric charges at rest and the electric fields and potentials they create. It deals with how stationary charges exert forces, store energy, and influence surrounding media, as well as how materials respond to electric fields. In electrostatics, changing magnetic fields are neglected, and Maxwell's equations reduce to a static form.

Coulomb's law gives the force between two point charges: F = k q1 q2 / r^2, with k = 1/(4π ε0). The electric field is defined as E = F/q and for a point charge q the field is E = k q / r^2 r_hat. The electric potential V satisfies E = -∇V, and the potential due to a point charge is V = k q / r. Gauss's law relates the flux of E through a closed surface to the enclosed charge: ∮ E·dA = Qenc/ε0, or in differential form ∇·E = ρ/ε0.

In materials, the field is reduced by the dielectric constant κ, and the permittivity is ε = κ ε0. Capacitance C = ε A/d stores energy U = 1/2 C V^2.

Charging methods include triboelectric charging (friction), conduction (contact with a charged body), and induction (rearranging charges without contact). Practical applications span air purification with electrostatic precipitators, electrostatic spray painting, and xerography in photocopiers and laser printers.

The study of electrostatics underpins safety considerations for static discharge and informs the design of sensors, capacitors, and various electrostatic devices.