Electronics components can be classified into either active or passive components, and there are multiple definitions used to classify components into these categories.
1. Active components
Definition 1 : Active components are those components which generate or supply energy to the circuit in some form. Components that can amplify power such as transistors also fall in this category since there is a net energy change in the circuit.
Definition 2 : Active components are the components connected to a source of energy and rely on it to amplify power (such as transistors).
Definition 3 : Active electronic components are those components that can control the flow of electricity (by either amplifying, attenuating, or generating.
Examples of active components
Examples of active components would be transistors, current sources, voltage sources, etc.
2. Passive components
Definition 1 : A passive component is a component that cannot generate, supply or amplify energy/power.
Definition 2 : Passive components are the components that do not require being connected to an external supply to operate.
Definition 3 : Passive electronic component are those components who cannot control the flow of electricity. For example, transformers cannot change the direction of electricity or have any control over it—they simply either increase voltage or current. The power remains constant.
Examples of passive components
Examples of passive components are resistors, inductors, transformers, etc.
Which definition of active and passive electronic components should be used?
There are multiple definitions and many opinions as to how these components work and what definition should be used to classify them as active or passive, and there is no clear consensus among the community. For example, some consider diode as an active component because it can control the flow of electricity by blocking a certain direction. However, there is also another group in electronics that considers diode a passive component because it does not generate or dissipate energy. Some consider diode an active component if the applied voltage across it is less than 0.7 V (or the forward bias voltage of that diode), otherwise they consider it as a passive component. Some also consider a diode with negative differential resistance an active component because that enables it to amplify signals, which is generally not the case for a diode.
We have learned that there are multiple definitions for the classification of electronic components into ‘active’ and ‘passive’. There are some components on which the electronic community has consensus — the obvious cases such as batteries or resistors —however, there are also some components such as diode which can not classified into active and passive components without considering external factors such as the type of diode, the voltage applied to the diode, the differential resistance of the diode and even then, there are disagreements in the community.