Active and Passive Elements

Active and Passive elements are two different types of circuit element. This classification is based on the capability of circuit element to deliver energy either in the form of voltage or current. If a circuit element has the capability to deliver energy to the circuit, it is called Active element whereas if the element consumes energy then it is called passive element. This article describes active and passive elements in electrical circuit.

What is Active Element?

An active element is defined as the circuit component which can enhance the energy level of a signal passing through it. Vacuum Tube, battery and semiconductor devices such as transistor, op-amp etc. are active element.

Active element is an essential component of circuit. This is because it provides necessary energy to other circuit component to work. These circuit components can control the flow of current through the circuit and sometime requires small voltage or current source to control its output current. Based on this, there are two types of active elements: Voltage Controlled and Current Controlled sources.

A voltage-controlled source is that whose output current is governed by its input voltage. Example of such type of active element is Bipolar Junction Transistor (BJT).

A current controlled elements are those whose output current is restrained by its input current.

What is Passive Element?

In simple words, any circuit element which only consumes power is called passive element. It cannot supply energy into the circuit. These components are incapable of providing any gain in energy and current. In fact, these elements require active element in the circuit to work. Example being resistor, inductor, capacitor, thermistor etc.

Passive element is just opposite to an active element. Former cannot inject energy into the circuit while the latter can inject energy. Apart from this, active element can control the flow of current through the circuit whereas a passive element can scale down the amount of current flow.

The above figure shows some circuit components. Can you tell which element is active and passive? Also, try to identify the unilateral and bilateral elements. Write your answer in comment box.