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.
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Elements vs. components
There is a distinction between real, physical electrical or electronic component 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
Any electrical network can be analyzed algebraically if its components are represented by a combination the following elements. Only 5 elements are required to represent any component or network:
- Two sources:
- Current source, measured in amperes - produces a current in a conductor.
- Voltage source, measured in volts - produces a potential difference between two points.
- Three passive elements:
- 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.
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.
