Kapasitans

Kapasitans, or capacitance, is the ability of an electrical system to store charge per unit of potential difference. It is defined as C = Q / V, where Q is the amount of charge and V is the voltage across the conductors. The SI unit is the farad (F); one farad equals one coulomb of charge per volt.

In simple structures, capacitance depends on geometry and the dielectric material between conductors. For a parallel-plate capacitor, C = ε0 εr A / d, where ε0 is the vacuum permittivity, εr is the dielectric relative permittivity, A is the plate area, and d is the separation. Materials with large εr or larger area increase capacitance; decreasing separation also increases it. Real devices differ from the ideal model due to fringing fields, temperature, dielectric losses, and aging.

Capacitance stores energy, with U = ½ C V^2. In alternating current (AC) circuits, capacitors oppose changes in voltage and are described by the capacitive reactance Xc = 1 / (2πfC). The impedance of an ideal capacitor is Z = 1 / (jωC). Capacitance can vary with frequency and temperature, and real capacitors exhibit leakage current and a dissipation factor representing losses.

Applications and types are diverse. Capacitors are used for energy storage, filtering, decoupling, timing, and power electronics. Common types include ceramic, film, electrolytic, tantalum, mica, and supercapacitors. Polarized electrolytic and tantalum capacitors require correct polarity; non-polar types are used for AC signals. Voltage rating and tolerance specify performance.

History and measurement: early devices such as the Leyden jar demonstrated capacitance, and the concept evolved with advances in electrical metrology. Modern definitions relate the farad to fundamental constants, while practical capacitors enable a wide range of electronic functions.