Circuit Components:
An circuit component is any basic discrete device or physical entity in a system used to affect electrons or their associated fields. These may be two types:
Active Components:
Those devices or components which produce energy in the form of Voltage or Current are called as Active Components. For more precise, an electrical element is called active, if it generates power and an electronic component is called active, if it can amplify or control power Example- generators, batteries, and operational ampliļ¬ers, transistors etc.
Passive Components:
Those devices or components which store or maintain or attenuate but can not generate or amplify energy in the form of Voltage or Current are known as Passive Components. Example- capacitor, inductor, resistor etc.
Difference between active and passive components:
1. Active devices inject power to the circuit, whereas passive devices are incapable of supplying any energy.
2. Active devices are capable of providing power gain (like amplifier), and passive devices are incapable of providing power gain.
3. Active device requires external source for its operations and passive device doesn't require any external source for its operation.
4. Sometimes some elements can be assumed as active and passive both. Then actually it depends on the context in which the component is used . This doesn't make things easier. Especially for diodes there are so many conflicting or different arguments: "In most cases (rectifier, Zener diode etc.) a diode is no doubt a passive device. Only in some special cases like with a tunnel diode, when its negative resistance region is used, it can be considered as an ACTIVE device." Because- it is an active device since it requires an external power source, to operate it in forward or reverse bias. It is an active device, since it can be used as an waveform generator (half wave rectifier). If the i-v characterisitic of the diode are in region I and III, then it is a passive device (always dissipating power). I think most diodes fall into this category. That's why the pn-junction device may be considered as an active device.
Another type of component is also used. This may be named as electromechanical components. Electromechanical components can carry out electrical operations by using moving parts or by using electrical connections. Example- Piezoelectric devices, crystals, resonators etc.