Circuit

An electrical circuit is a closed path that allows electric charge to flow between sources and loads. It consists of a power source, conductors, and interconnecting components such as resistors, capacitors, inductors, and active devices (diodes, transistors, integrated circuits). Circuits are designed to accomplish functions such as delivering power, amplifying signals, filtering frequencies, switching, or performing computing operations. A circuit must be closed to sustain current; an open circuit prevents current flow, while a short circuit creates a low-resistance path that can cause excessive current.

Circuit diagrams (schematics) use standardized symbols to represent components and connections. Analysis typically relies on Kirchhoff's laws, which state that current entering a node equals leaving (Kirchhoff's current law) and that the sum of voltages around any loop is zero (Kirchhoff's voltage law), together with Ohm's law for resistive elements. Circuits may be linear or nonlinear, time-invariant or time-varying, analog or digital. They can be arranged in series, in parallel, or in mixed configurations; their behavior is described by differential or difference equations and often simulated with tools such as SPICE.

In practice, circuits are built on breadboards or printed circuit boards and tested under safety standards. They underpin modern electronics, communications, and power systems from microchips to grid-scale networks. The term circuit also appears in other domains to denote a closed route or loop, such as a race circuit or a cycle in a graph.