Types of Network Elements - Electric Circuit

In this article, we will study about the network or circuit elements and the classification of network elements.

Network Element

A network element is the basic building block of an electrical network. The network element is sometimes also called a circuit element or circuit component.

A network element can be defined as a mathematical model of an electrical device and is characterized by its voltage and current relationship. Also, a network element or circuit element cannot be further divided into a device. Thus, the network element is the most fundamental component of an electrical system.

Classification of Network Elements

Based on the behavior of a network element in the circuit, the network elements are classified into the following types:

• Active Elements
• Passive Elements
• Bilateral Elements
• Unilateral Elements
• Linear Elements
• Non-Linear Elements
• Lumped Elements
• Distributed Elements

(1). Active Elements

When a network element or circuit element has the ability to deliver electrical energy or to produce power gain in the circuit, then the element is called an active element.

In other words, a circuit element for which the slope of its characteristics curve at any point is negative then the element is called an active element.

Common examples of active elements are generators, batteries, other independent sources, transistors, Op-Amps, etc.

The active elements are able to provide power or power gain to the electric circuit for an infinite duration of time.

Note – The transistor (BJT) can provide power amplification or power gain in the circuit so it is an active element, while the transformer has the same power at input terminals and output terminals, hence the transformer is not an active element.

(2). Passive Elements

A circuit element that can only absorb electric power is called a passive element. The passive elements are not able to deliver the electric power or power gain to the circuit.

In other words, if the slope of the characteristics curve of an electric circuit element is positive at all the points, then the element is a passive element.

Examples of passive elements are resistors, inductors, capacitors, transformers, etc.

Note – The charged inductor and capacitor provide power to the circuit but for a very small time, i.e. they cannot provide power or power gain for an infinite duration of time which is why they are passive circuit elements.

(3). Bilateral Elements

The elements for which the relationship between voltage and current remains the same for current flowing in either direction are known as bilateral elements.

Therefore, for the bilateral elements, the characteristics curve is similar in the opposite quadrants.

Examples of bilateral elements are resistors, inductors, and capacitors.

(4). Unilateral Elements

The circuit elements that exhibit the different relationship between current and voltage for two directions (forward and reverse) of the current are called unilateral elements.

Hence, for the unilateral elements, the characteristics curve is different in opposite quadrants.

A PN junction diode is the most common example of a unilateral circuit element.

(5). Linear Elements

An electric circuit element that follows linearity property (i.e. homogeneity and superposition properties) for the relationship between excitation (input) and response (output), is called a linear element.

For a linear element, the characteristics curve is always a straight line that passes through the origin. 

The most common example of a linear element is an ohmic resistor.

Linearity Property:

The property of a circuit element that describes a linear relationship between excitation (input) and response (output) is known as the linearity property. The linearity property is a combination of two sub-properties namely the homogeneity (scaling) property and superposition (additivity) property.

Homogeneity Property – According to the homogeneity property, if the input is scaled (or multiplied) by a constant (say α), then the output also gets scaled (or multiplied) by the same constant (α), i.e.

For excitation E(t) and response R(t), we have,

`\E(t)→R(t)`

`\∴αE(t)→αR(t)`

Superposition Principle – According to the superposition principle or additivity property, the output corresponding to a sum of inputs is equal to the sum of the outputs to each input applied separately, i.e.

`\"If "E_1 (t)→R_1 (t)" and "E_2 (t)→R_2 (t)`

Then, according to the superposition principle,

`\E_1 (t)+E_2 (t)→R_1 (t)+R_2 (t)`

(6). Non-Linear Elements

The circuit elements that do not follow the linearity property (i.e. homogeneity and superposition) for the relationship between input and output are called non-linear elements.

In simple words, those elements which are not linear are called non-linear elements.

For the non-linear elements, the characteristics curve may not be a straight line or it may not pass through the origin.

Examples of non-linear elements include diodes, transistors, vacuum tubes, etc.

(7). Lumped Elements

A circuit element is considered a lumped element is its physical size is very small with respect to the wavelength of the signal. Therefore, the separate elements that are very small in size are called lumped elements.

Examples of lumped elements are resistors, capacitors, and inductors.

(8). Distributed Elements

A distributed element is one that is distributed over the entire length of the circuit and is not electrically separable. One practical example of a distributed element is transmission lines.

In the case of transmission lines, the resistance, capacitance, and inductance are distributed over the entire length of the line and it is not possible to consider it at a single point.

Note – At the steady state, we can consider a distributed element as a lumped element.

Therefore, this is all about the network or circuit elements and the classification of circuit elements.