A circuit element is the fundamental building block of a circuit. It can be defined as a mathematical model of a two-terminal electrical device and can be characterized by its voltage–current relationship. Also, a circuit element can never be further divided into other two-terminal devices.
In this article, we will learn the classification of circuit elements (network elements).
Classification of Circuit Elements
Different types of circuit elements are described below.
Resistor
When the voltage across the terminals of the circuit element is directly proportional to the current flowing through it, then this circuit element is called a resistor.
Inductor
When the voltage across the terminals of the circuit element is directly proportional to the time derivative of current through it, then this circuit element is called an inductor.
Capacitor
When the voltage across the terminals of the circuit element is directly proportional to the time integral of the current through it, then this circuit element is referred to as a capacitor.
Independent Source
If the voltage across the terminals of the element is completely independent of the current or the current through the element is completely independent of the voltage across its terminals, then this element is referred to as an independent source. It can be an independent voltage source or an independent current source.
Dependent Source
When the output voltage or current of the circuit element is the function of a current or voltage in any other part of the circuit, then this element is known as a dependent source. It can be a dependent voltage source or a dependent current source.
Passive Elements
Those circuit elements that always absorb power or cannot produce power gain in the circuit are known as passive elements.
Examples of passive elements are resistor, inductor, capacitor, transformer, etc.
Active Elements
Those circuit elements that can deliver power to the circuit or can produce a power gain in the circuit for an infinite duration of time are known as active elements.
Examples of active elements are generators, independent sources, transistors, op-amps, etc.
Bilateral Elements
A circuit element for which the voltage-current relationship is the same for current flowing in both directions is known as a bilateral element. Hence, bilateral elements behave equally in either direction.
Examples of bilateral elements include resistor, inductor, and capacitor.
Unilateral Elements
A unilateral element is one which has a different voltage-current relationship depending on the direction of the current flow. Therefore, a unilateral element behaves differently in different directions.
Examples of unilateral elements are diodes, transistors, vacuum tubes, etc.
Lumped Elements
We can define lumped elements as follows:
Those circuit elements which are of very small size and are physically separable are known as lumped elements.
Or
When the physical size of the circuit element is negligibly small as compared to the wavelength of the signal, then the circuit element is known as a lumped element.
Examples of lumped elements include resistor, inductor, and capacitor.
Distributed Elements
We can define distributed elements as follows:
When the elements are distributed over the entire length of the circuit and are not possible to separate electrically are called distributed elements.
Or
When the physical size of the circuit element is comparable with the wavelength of the signal, then it is called a distributed element.
Examples of distributed elements are transmission lines because the transmission lines have resistance, inductance, and capacitance, but it is not possible to separate these elements from the line. Hence, the transmission lines are examples of distributed elements.
Linear Elements
Those circuit elements which have a response directly proportional to the applied excitation are known as linear elements.
Or
A linear element is one whose output-to-input relationship can be described by a linear differential equation.
Or
Those circuit elements that follow additivity and homogeneity properties (combinedly known as linearity property) for the relationship between excitation and response are known as linear elements.
Examples of linear elements are pure resistor, inductor, and capacitor.
Non-Linear Elements
Those circuit elements that do not follow the linearity property (additivity and homogeneity properties) for the relationship between excitation and response are known as non-linear elements.
Examples of diodes, op-amps, memristors, ferrite inductors, etc.
Important Notes
- The transformer is a passive element because it has the same power at input and output.
- The transistor is an active element as it can provide power gain in the circuit through amplification.
- At a steady state, the distributed elements can be considered as lumped elements.
Conclusion
So, this is all about the classification of circuit elements (network elements). If you have any questions related to this topic, kindly let me know in the comment section. I will answer shortly.