What is the main feature of active components in electrical circuits?

Active components in electrical circuits are distinguished primarily by their ability to amplify signals and their requirement for an external power source. These components, such as transistors, operational amplifiers, and integrated circuits, can control and manage voltage and current in a way that passive components cannot.

For example, a transistor can amplify a small input signal into a much larger output signal, thus playing a crucial role in various applications such as signal processing and audio amplification. The necessity for a power source is fundamental since these components need external energy to perform their function effectively. Without this power, active components would be unable to operate, unlike passive components, which can function without a power supply but do not have the ability to amplify signals.