Which statement is true about rheostats?

Rheostats are specialized variable resistors designed to control current by adjusting resistance, making the statement that they are primarily used to resist current accurate. This is their fundamental purpose, as rheostats allow for the modification of resistance in a circuit to regulate the flow of electrical current, which can be crucial in various applications such as dimming lights or controlling motor speed.

In contrast, while rheostats may be used in series configurations, it is not universally true that they are always used that way, as they can also be arranged in parallel in certain circuits. The claim about their ability to handle higher voltage than potentiometers is not definitive, as the actual voltage handling can depend on the specifications of the individual components. Additionally, rheostats are designed specifically to alter resistance; hence, they can indeed change resistance values through physical adjustments, refuting that they cannot change resistance at all.