Which component is primarily used for signal amplification?

The transistor is primarily used for signal amplification due to its ability to control a large output current based on a smaller input current. This is achieved through the transistor's three terminals: the collector, base, and emitter. When a small signal is applied to the base terminal, it modulates the current flow between the collector and emitter, enabling the transistor to amplify the input signal.

Transistors are foundational in various electronic circuits, including audio amplification and radio transmission, allowing for the enhancement of weak signals to a more usable level. Unlike resistors, capacitors, and inductors, which either resist, store, or convert electrical energy, the transistor actively increases the strength of an electrical signal, making it a key component in amplification processes.