What is the function of a rheostat?

A rheostat is designed specifically to provide a variable amount of resistance within an electric circuit. This feature allows it to adjust the flow of current as needed, which is beneficial in applications where the intensity of the current needs to be controlled, such as in dimming lights or controlling motors. By varying the resistance, the rheostat can influence how much current flows, thereby changing the output to suit specific requirements.

Fixed resistance, like that referenced in the first option, is not a characteristic of a rheostat but rather of a resistor. Additionally, measuring voltage is a function associated with voltmeters, not rheostats, and converting alternating current (AC) to direct current (DC) is the role of rectifiers. Thus, the ability of a rheostat to change resistance dynamically is what makes it useful and distinguishes it from other components in electrical circuits.