What type of resistor is known as a variable resistor used to control current?

A variable resistor specifically designed to control current is known as a rheostat. Rheostats allow for the adjustment of resistance in an electric circuit without interrupting the flow of current, effectively enabling control over voltage and current levels. This capability makes them particularly useful in applications where the brightness of lights or speed of motors needs to be modulated.

In contrast, a capacitor stores electrical energy temporarily and does not adjust current. A transformer is used to change the voltage level in an alternating current (AC) circuit, while a rectifier converts AC to direct current (DC). Each of these components serves a distinct purpose in electronics, unlike the rheostat, which directly alters resistance and thus current flow.