Which component is commonly used in amplifiers to increase signal strength?

The component that is commonly used in amplifiers to increase signal strength is the transistor. Transistors serve as the fundamental building blocks in many electronic circuits, especially amplifiers, due to their ability to control the flow of electrical current. When a small input signal is applied to the transistor's control terminal (the base in the case of a bipolar junction transistor), it allows a larger current to flow from the collector to the emitter, effectively amplifying the input signal.

Transistors can amplify both analog and digital signals, making them crucial in a wide variety of applications, from audio equipment to communication devices. They can operate in different modes, such as common emitter, common collector, or common base configurations, each providing varying degrees of amplification and input/output characteristics.

In contrast, resistors are used primarily to limit current flow and set biasing conditions, capacitors serve to store and filter signals rather than amplify them, and inductors are used for energy storage in magnetic fields and are typically involved in tuning circuits rather than direct signal amplification. Thus, among the options listed, the transistor is uniquely capable of increasing signal strength, which solidifies its role in amplifier circuits.