Classification of Network Elements - Active, Passive, Linear & Non-linear

An element is the basic building block of an electrical network or circuit. An electrical network is an interconnection of different electrical elements, components, input signals, and output signals. All these elements are connected by wires forming a closed path to flow the current. In this article let us see the classification of electrical network elements with examples.

Classification of Network Elements :

Based on the behavior and characteristics electric network elements are classified as,
  • Active and Passive Elements
  • Linear and Non-linear Elements
  • Unilateral and Bilateral Elements
  • Lumped and Distributed Elements.

Classification of Network Elements

Active Elements :

The active elements are one which supplies energy or having capable of generating energy. Active elements are also known as energy sources. Energy sources (voltage sources or current sources), battery, alternator or dc generator, transistor, diode (with negative differential resistance), LED, photodiode, and SCR are some examples of active elements.

A source that produces a potential difference across its terminal is called a voltage source. A voltage source that maintains constant potential difference and is independent of the current drawn is called Ideal Voltage Source. An ideal voltage source has zero internal resistance. However, in practice, it is difficult to have an ideal voltage source.

A current source delivers current in a circuit of a given magnitude which is independent of potential difference or voltage developed across its terminals. Similar to an ideal voltage source, an ideal current source delivers constant current irrespective of the voltage and other circuit parameters. An ideal current source has infinite internal resistance.

A discharging battery supply continues energy in a circuit for a long period. Thus battery is considered an active element. Since a transistor can be used for amplifying a signal. A transistor is also considered an active element. Generally, diodes are passive components, but a diode with negative differential resistance can be used to amplify the signal which in turn makes them an active element.

Passive Elements :

The elements which can either store or dissipates energy are called Passive Elements. Unlike active element, passive elements do not generate energy or provide amplification rather they consume energy and stores it in the form of electrostatic or electromagnetic fields or dissipates it in the form of heat. Some examples of passive elements are resistors, inductors, capacitors, transformers, diodes, etc.

A resistor is used to limit the current flowing in a circuit or can also be used as a voltage divider. It converts the current flowing through it into heat. A transformer converts a voltage from one level to another level but the power remains the same on both the primary and secondary sides.

An inductor stores energy in the form of an electromagnetic field whereas a capacitor stores energy in the form of an electrostatic field. Both the inductor and capacitor observe and stores energy which is limited and transient. Since no energy is being generated and amplified in the resistor, inductor, capacitor, and transformer they are considered as the passive elements.

Unilateral Elements :

The circuit elements whose characteristics change with a change in direction of current flowing through it are called Unilateral Elements. A unilateral element allows current only in one direction. If the direction of the current changes, either it opposes the current flow or there will be a change in its behavior. The impedance of unilateral elements varies with variations in the flow of current.

A diode and transistor are examples of unilateral elements. We know that a diode conducts only in forward-bias condition i.e. when P-side is at a higher potential than the N-side. During the reverse bias state, a diode acts as an open circuit.

Bilateral Elements :

A bilateral element is one whose characteristics or behavior remain same in both directions of current flow i.e., even if the direction of current changes V-I characteristics of the element remain same. A bilateral element allows current through it in both directions. The resistance/impedance of bilateral elements remains same in both directions of current flow. Some examples of bilateral elements are resistors, inductors, capacitors, TRAIC, etc.

A resistor is a bilateral element because it allows current in both directions. The value of current and voltage across the resistor remains same even if the direction of the current changes.

Similarly, there is no specific terminal for an inductor and capacitor, the properties remain same even when the direction of the current changes. A TRAIC is also considered a bilateral device since it conducts current in either direction when triggered.

Linear Elements :

Linear elements are those whose value doesn't change with current or voltage. The V-I characteristics of linear elements will be a straight line and always passes through the origin. Linear elements obey the law of superposition and homogeneity. They obey the properties of Ohm's law. Some examples of linear elements are resistance, inductor, and capacitor.

When the current through the resistor is doubled, the voltage across it will be doubled but the value of resistance will be constant. Similarly, the capacitor value remains constant when voltage is applied to store the charge. Inductors with ceramic, ferrite, and air core have linear properties.

Non-linear Elements :

The circuit elements whose value varies with respect to current and voltage (i.e., circuit parameters doesn't remain constant) is called Non-Linear Element. The current flowing and voltage across these elements have a non-linear relationship.

Non-linear elements do not satisfy homogeneity and superposition laws. The plot between the voltage and current of non-linear elements will not be a straight line like linear elements. Some examples of non-linear elements are diodes, transistors, saturated iron core inductors and transformers, modulators, etc.

Lumped Elements :

The network elements which are concentrated in one place or located at a small place in the circuit are called Lumped Elements. Lumped elements can be separable in the network. The resistance, inductance, and capacitance connected in any electrical circuit can be said as lumped elements.

Distributed Elements :

The elements which are distributed throughout the network instead of concentrating in one place are called Distributed Elements. Distributed elements cannot be separable in the network. The resistance, inductance, and capacitance of a transmission line are examples of distributed elements.

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