punktlaengu

In Estonian, punktlaeng refers to a point charge, and the form punktlaengu is the genitive form meaning “of a point charge.” In physics, a point charge is an idealized model of an electrically charged object with negligible size, used to simplify the analysis of electric fields and potentials.

A single point charge q located at position r0 creates an electric field E at any other point r given by E(r) = (1/(4πε0)) q (r − r0) / |r − r0|^3, where ε0 is the vacuum permittivity. The magnitude of the field is E = (1/(4πε0)) |q| / |r − r0|^2 and the field points radially away from the charge if q is positive (and toward the charge if q is negative). The electric potential V at r is V(r) = (1/(4πε0)) q / |r − r0|, assuming V → 0 as |r − r0| → ∞. The electric potential energy of a test charge q0 placed at r is U = (1/(4πε0)) q q0 / |r − r0|.

The concept extends by superposition: the field of multiple point charges is the vector sum of the fields from each charge. Gauss’s law relates the field to charge distribution, with the charge density for a single point charge described by ρ(r) = q δ(r − r0). While the point charge model is highly useful, it is an idealization; real charges have finite size, and at very small distances or high energies more detailed models are required.