What type of component is often used as an adjustable volume control?

A potentiometer is specifically designed to control the level of voltage or current in a circuit, making it an ideal component for adjustable volume control applications, such as in audio equipment. It consists of a resistive element and a sliding contact (or wiper) that moves along the element. By adjusting the position of the wiper, users can vary the resistance in the circuit, which effectively changes the volume of the audio signal.

In contrast, a fixed resistor provides a constant resistance and cannot be altered to change volume levels. A power resistor is designed to handle high power loads and, similarly to fixed resistors, does not provide adjustability for volume control. A transformer, on the other hand, is used primarily for voltage transformation and electrical isolation, not for controlling audio levels. Thus, the unique design and function of a potentiometer make it the correct choice for volume control applications.