Electrical element

Electrical elements are conceptual abstractions representing idealized electrical components, such as resistors, capacitors, and inductors, used in the analysis of electrical networks. All electrical networks can be analyzed as multiple electrical elements interconnected by wires. Where the elements roughly correspond to real components the representation can be in the form of a schematic diagram or circuit diagram. This is called a lumped element circuit model. In other cases infinitesimal elements are used to model the network in a distributed element model.

These ideal electrical elements represent real, physical electrical or electronic components but they do not exist physically and they are assumed to have ideal properties, while actual electrical components have less than ideal properties, a degree of uncertainty in their values and some degree of nonlinearity. To model the nonideal behavior of a real circuit component may require a combination of multiple ideal electrical elements in order to approximate its function. For example, an inductor circuit element is assumed to have inductance but no resistance or capacitance, while a real inductor, a coil of wire, has some resistance in addition to its inductance. This may be modeled by an ideal inductance element in series with a resistance.

Circuit analysis using electric elements is useful for understanding many practical electrical networks using components. By analyzing the way a network is affected by its individual elements it is possible to estimate how a real network will behave.


Circuit elements can be classified into different categories. One is how many terminals they have to connect them to other components:

Elements can also be divided into active and passive:

Another distinction is between linear and nonlinear:

One-port elements

Only nine types of element (memristor not included), five passive and four active, are required to model any electrical component or circuit. Each element is defined by a relation between the state variables of the network: current, ; voltage, , charge, ; and magnetic flux, .

in this relationship does not necessarily represent anything physically meaningful. In the case of the current generator, , the time integral of current, represents the quantity of electric charge physically delivered by the generator. Here is the time integral of voltage but whether or not that represents a physical quantity depends on the nature of the voltage source. For a voltage generated by magnetic induction it is meaningful, but for an electrochemical source, or a voltage that is the output of another circuit, no physical meaning is attached to it.
Both these elements are necessarily non-linear elements. See #Non-linear elements below.
These four elements are examples of two-port elements.

Non-linear elements

Conceptual symmetries of resistor, capacitor, inductor, and memristor.

In reality, all circuit components are non-linear and can only be approximated to linear over a certain range. To more exactly describe the passive elements, their constitutive relation is used instead of simple proportionality. From any two of the circuit variables there are six constitutive relations that can be formed. From this it is supposed that there is a theoretical fourth passive element since there are only five elements in total (not including the various dependent sources) found in linear network analysis. This additional element is called memristor. It only has any meaning as a time-dependent non-linear element; as a time-independent linear element it reduces to a regular resistor. Hence, it is not included in linear time-invariant (LTI) circuit models. The constitutive relations of the passive elements are given by;[1]

where is an arbitrary function of two variables.

In some special cases the constitutive relation simplifies to a function of one variable. This is the case for all linear elements, but also for example, an ideal diode, which in circuit theory terms is a non-linear resistor, has a constitutive relation of the form . Both independent voltage, and independent current sources can be considered non-linear resistors under this definition.[1]

The fourth passive element, the memristor, was proposed by Leon Chua in a 1971 paper, but a physical component demonstrating memristance was not created until thirty-seven years later. It was reported on April 30, 2008, that a working memristor had been developed by a team at HP Labs led by scientist R. Stanley Williams.[2][3][4][5] With the advent of the memristor, each pairing of the four variables can now be related.

There are also two special non-linear elements which are sometimes used in analysis but which are not the ideal counterpart of any real component:

These are sometimes used in models of components with more than two terminals: transistors for instance.[1]

Two-port elements

All the above are two-terminal, or one-port, elements with the exception of the dependent sources. There are two lossless, passive, linear two-port elements that are normally introduced into network analysis. Their constitutive relations in matrix notation are;


The transformer maps a voltage at one port to a voltage at the other in a ratio of n. The current between the same two port is mapped by 1/n. The gyrator, on the other hand, maps a voltage at one port to a current at the other. Likewise, currents are mapped to voltages. The quantity r in the matrix is in units of resistance. The gyrator is a necessary element in analysis because it is not reciprocal. Networks built from the basic linear elements only are obliged to be reciprocal and so cannot be used by themselves to represent a non-reciprocal system. It is not essential, however, to have both the transformer and gyrator. Two gyrators in cascade are equivalent to a transformer but the transformer is usually retained for convenience. Introduction of the gyrator also makes either capacitance or inductance non-essential since a gyrator terminated with one of these at port 2 will be equivalent to the other at port 1. However, transformer, capacitance and inductance are normally retained in analysis because they are the ideal properties of the basic physical components transformer, inductor and capacitor whereas a practical gyrator must be constructed as an active circuit.[6][7][8]


The following are examples of representation of components by way of electrical elements.

See also


  1. 1 2 3 Ljiljana Trajković, "Nonlinear circuits", The Electrical Engineering Handbook (Ed: Wai-Kai Chen), pp.75–77, Academic Press, 2005 ISBN 0-12-170960-4
  2. Strukov, Dmitri B; Snider, Gregory S; Stewart, Duncan R; Williams, Stanley R (2008), "The missing memristor found", Nature, 453 (7191): 80–83, Bibcode:2008Natur.453...80S, doi:10.1038/nature06932, PMID 18451858
  3. EETimes, 30 April 2008, 'Missing link' memristor created, EETimes, 30 April 2008
  4. Engineers find 'missing link' of electronics – 30 April 2008
  5. Researchers Prove Existence of New Basic Element for Electronic Circuits – 'Memristor' – 30 April 2008
  6. Wadhwa, C.L., Network analysis and synthesis, pp.17–22, New Age International, ISBN 81-224-1753-1.
  7. Herbert J. Carlin, Pier Paolo Civalleri, Wideband circuit design, pp.171–172, CRC Press, 1998 ISBN 0-8493-7897-4.
  8. Vjekoslav Damić, John Montgomery, Mechatronics by bond graphs: an object-oriented approach to modelling and simulation, pp.32–33, Springer, 2003 ISBN 3-540-42375-3.
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