Which component is typically used for switching and amplifying electrical signals?

The bipolar junction transistor (BJT) is commonly used for switching and amplifying electrical signals due to its ability to control a larger current flow between its collector and emitter terminals, based on a smaller current input at its base terminal. This property makes the BJT versatile in various applications, such as in amplifiers where it can boost signal strength, or in digital circuits where it acts as a switch to control the flow of electricity.

In contrast, a resistor is designed to limit the flow of current in a circuit but does not switch or amplify signals. A diode allows current to flow in one direction and is primarily used for rectification rather than amplification or switching applications. A capacitor stores electrical energy temporarily and releases it but does not amplify or switch signals directly. This shows that the BJT uniquely serves a dual function of switching and amplifying, making it the correct choice for the question.