Electrical element

From Wikipedia, the free encyclopedia

Electrical components.

The concept of electrical elements is used in the analysis of electrical networks. Any electrical network can be modeled by decomposing it down to multiple, interconnected electrical elements in a schematic diagram or circuit diagram. Each electrical element affects the voltage in the network or current through the network in a particular way. By analyzing the way a network is affected by its individual elements, it is possible to estimate how a real network will behave on a macro scale.

Elements vs. components

There is a distinction between real, physical electrical or electronic components and the ideal electrical elements by which they are represented.

• Electrical elements do not exist physically, and are assumed to have ideal properties according to a lumped element model.
• Conversely, components do exist, have less than ideal properties, their values always have a degree of uncertainty, they always include some degree of nonlinearity and typically require a combination of multiple electrical elements to approximate their functions.

Circuit analysis using electric elements is useful for understanding many practical electrical networks using components.

The elements

The four fundamental circuit variables are current, I; voltage, V, charge, Q; and magnetic flux, Φ_m. Only 5 elements are required to represent any component or network by manipulating these four variables:

• Two sources:
  • Current source, measured in amperes - produces a current in a conductor. Affects charge according to the relation dQ = − Idt.
  • Voltage source, measured in volts - produces a potential difference between two points. Affects magnetic flux according to the relation dΦ_m = Vdt.
• Three passive elements:
  • Resistance R, measured in ohms - produces a voltage proportional to the current flowing through it. Relates voltage and current according to the relation dV = RdI.
  • Capacitance C, measured in farads - produces a current proportional to the rate of change of voltage across it. Relates charge and voltage according to the relation dQ = CdV.
  • Inductance L, measured in henries - produces a voltage proportional to the rate of change of current through it. Relates flux and current according to the relation dΦ_m = LdI.

A fourth component, the memristor, has been proposed but is not generally accepted as one of the basic circuit elements.^{[citation needed]} It was reported on April 30, 2008, that a working memristor has been developed by HP.^[1][2][3][4] It would have a memristance M, and would relate magnetic flux and charge by dΦ_m = MdQ, so that every pair of variables would be related.

Examples

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

• On a first degree of approximation, a battery is represented by a voltage source. A more refined model also includes a resistance in series with the voltage source, to represent the battery's internal resistance (which results in the battery heating and the voltage dropping when in use). A current source in parallel may be added to represent its leakage (which discharges the battery over a long period of time).
• On a first degree of approximation, a resistor is represented by a resistance. A more refined model also includes a series inductance, to represent the effects of its lead inductance (resistors constructed as a spiral have more significant inductance). A capacitance in parallel may be added to represent the capacitive effect of the proximity of the resistor leads to each other. A wire can be represented as a low-value resistor
• Current sources are more often used when representing semiconductors. For example, on a first degree of approximation, a bipolar transistor may be represented by a variable current source that is controlled by the input voltage.

References

See also

Wikimedia Commons has media related to:

Electronic devices

• electrical or electronic component