Active and Passive Devices

Active Device

Active devices are those devices which needs a source of energy, and can inject power into the circuit. This shows that it controls electricity electrically. This makes the basics for ELECTRONICS - which is electron mechanics. Active component in the circuit makes its electronic. These devices provide a mechanism to control flow of electron through  the external source. This makes them to change energy flowing through them and this is the reason for amplifiers and rectifiers etc.

Some are: Transistors, Diodes, Vacuum Tubes, Integrated Circuits.

What is the mechanism involved?

The mechanism of external source to control the electron flow would be voltage or current, and are not surprisingly known as voltage-controlled active devices and current-controlled active devices.

Passive Device

These are those which neither inject power to the circuit nor require energy for functioning. The energy present in the circuit is enough for its functioning. But they are useful in storing or dissipating energy in one or the other form required by the circuit for proper operation.

Some are: Resistors, Capacitors, Inductors.