What is the use of a variable resistor?

A variable resistor, commonly known as a potentiometer, serves the primary function of adjusting resistance levels within a circuit. This adjustability allows for fine-tuning of voltage and current signals, enabling control over factors like brightness in lighting circuits, volume in audio applications, or other parameters that require variation in resistance.

When you change the position of the wiper on a potentiometer, it alters the resistance between the wiper and the endpoints, thus varying the output voltage or current according to the needs of the circuit. This feature is essential in many electronic devices, making variable resistors versatile components in various applications like audio equipment, consumer electronics, and even control systems.

The other choices suggest functions that do not align with the purpose of a variable resistor, such as fixing resistance levels, generating electrical current, or increasing voltage, all of which are outside the scope of a variable resistor's designed capabilities.