Circuits

A circuit is a closed path that allows electric current to flow, formed by interconnecting elements such as sources, conductors, and loads. Circuits can be simple or complex and are described by basic electrical quantities such as current, voltage, and impedance. They are analyzed using established circuit theory and laws that relate these quantities.

Common components include voltage or current sources, resistors, capacitors, inductors, diodes, transistors, and switches. Passive components store or dissipate energy, while active components provide power or amplification. Electrical circuits deal with macroscopic phenomena and can be purely passive, while electronic circuits incorporate active devices and are used to process signals. Digital circuits use logic gates and operate with discrete voltage levels, whereas analog circuits handle continuous signals.

Basic configurations include series and parallel connections. In a series circuit the same current flows through all elements and the total voltage is the sum of voltage drops; in a parallel circuit the voltage is the same across elements and the currents add. Key tools for analysis include Ohm's law (V = IR) and Kirchhoff's laws (current and voltage), as well as network theorems such as Thevenin and Norton equivalents. More advanced analysis uses nodal or mesh methods and may examine frequency response using impedance.

Circuits underpin power delivery, consumer electronics, communications, sensing, and computing. They appear as printed circuit boards, integrated circuits, or discrete assemblies. The theoretical basis rests on laws from physics developed in the 19th and early 20th centuries, notably Ohm's and Kirchhoff's work and Maxwell's equations, which describe how electric fields and currents propagate and interact in conductors and devices.