An electric circuit, or electrical network, consists of electrical elements or components connected by conductors. Elements include devices (such as an inductor, resistor, capacitor, conductor, line, or cathode ray tube) with terminals at which it may be connected directly with other devices. It can also mean a antenna radiator (either parasitic or active). In circuitry, it can be used to specify a portion of a integrated circuit that contributes directly to the IC's operation.
Main article: lumped element model.
The elements alter the way that electric current flows through the conductors. The concept of electrical elements is used in the analysis of electrical networks. Each element represents one of the fundamental aspects of the electrical network.
The elements are:
Current source, measured in amperes - produces a current in a wire.
Voltage source, measured in volts - produces a potential difference across two points.
Resistance, measured in ohms - produces a voltage proportional to the current flowing through it.
Capacitance, measured in farads - produces a current proportional to the rate of change of voltage across it.
Inductance, measured in henries - produces a voltage proportional to the rate of change of current through it.
Any electrical circuit can be analysed if the circuit components are represented by the above elements. However, there is a distinction between elements, and the components which the elements represent.
Elements and Components
A battery provides electromotive force (emf), or voltage, in a circuit. It contains layers of chemicals that cause electrons to move in a certain direction, from its negative pole to its positive pole. It is marked with a rating of how much voltage there is across the two poles, and a (-) for the negative pole and a (+) for the positive pole. Batteries may also be marked with an ampere hour (Ah) rating, indicating total charge capacity.
An ideal battery can thus be represented as a voltage source. In practice, a battery also has an internal resistance that is represented as a resistance in series with the voltage source.
If a wire is used to connect the two poles of a battery, electrons flow through the wire from the negative end to the positive end. (The wire will also get hot because it isn't a perfect conductor, and the battery will quickly exhaust all its power.) Thus a wire can be represented as a low-value resistor.
Current sources are often absent from basic electric circuits, and are more likely to be found in electronic circuits containing semiconductors.
A resistor is a component whose function is to regulate the current in the circuit. One common kind is a little cylinder of graphite with metal wires coming out of either end. These are painted with colored stripes that indicate the resistance, in ohms, and the tolerance, in percent. This system is called the resistor color code.
Another kind of resistor is a filament, which is a coil of metal wire that can withstand high temperature but has a finite resistance. When a current is passed through a filament, it heats up because of this resistance. Filaments are commonly used in light bulbs and heaters. They are marked with the voltage that should be applied to them, and the power, in watts, that they will then give off as light and heat. Due to the effect of heating, a filament's resistance is higher when it is hot than when it is cold.
An electric charge can be stored and then quickly released by a component called a capacitor. A common type of capacitor consists of two pieces of metal foil (or plates) with an insulator (the dielectric) such as waxed paper between them.
If an electric charge is placed on the plates of a capacitor, it will stay there because it can't cross the insulator to the other plate. If a wire is then connected between the two plates, the charge will flow through the wire to balance the charges on the opposite plates--the capacitor is then said to be discharged.
Some capacitors look like a cylinder or blob with two wires coming out one end, and are marked to indicate their capacitance (the charge that they store per volt) in microfarads (μF), nanofarads (nF) or picofarads (pF).
Inductance in a circuit is provided by components called inductors, which are almost always built from coils of wire. Large values of inductance are obtained by forming the coil around a magnetic core, such as a lump of iron or ferrite. Inductance is also present in the windings of electric motors and generators, and to a lesser extent in any piece of wire.
A longer list of electronic components can be found in the electronics article.