An Electrical Circuit and Its Elements

An electrical circuit is a combination of devices for running an electrical current. Electromagnetic processes can be described in such terms as current, voltage (potential difference) electromotive force, charge, magnetic flux, resistance, inductance, mutual inductance and capacitance.

The main elements of a circuit are sources and loads of electrical energy (signals).

The power sources and signal sources are intended for converting various kinds of energy into electrical energy (turbo and hydrogenerators, accumulators, electron generators, etc.).

The loads of energy (signals) are used for converting electrical energy into other kinds of energy (electrical motors, electrical furnaces, electron-beam tubes, etc.).

Besides these main elements, the circuit contains various auxiliary elements, which connect sources with loads (lines of transmission, connective wires), suppress or strengthen certain components of the signal (filters, amplifiers), charge the magnitudes of voltages and currents (transformers) and so on.

There are two kinds of circuits: the first circuits are intended for transmitting and converting electrical energy (these circuits are used in electro-power engineering) and the second circuits are intended for transmitting and transforming information (these circuits are used in communication engineering, radio engineering, devices of automation and telemechanics, etc.).

Each element of a circuit has a certain number of terminals (poles) in order to connect this element with other elements. Two-pole elements have two terminals. Power sources (except multiphase sources), resistors, capacitors, inductance coils are two-pole elements. Three-pole elements are electron lamps (vacuum triodes) and transistors (semiconductive triodes). Four-pole elements are two-winding transformers, integral operational amplifiers. The elements of a circuit having more than four terminals are multiwinding transformers, various micro-modules, solid-state components of electron schemes, etc. Three-pole, four-pole elements and so on are called multipole elements.

We distinguish active and passive elements of a circuit. The power and signal sources are active elements. We also consider electron lamps, transistors, operational amplifiers as active elements, which are capable to strengthen an electrical signal. The energy is dissipated or accumulated (resistors, inductive coils, capacitors, transformers) in the passive elements.