A rheostat is least likely to be used in connection with the operation of?

A rheostat is a type of variable resistor used primarily to control current in electric circuits. It operates by adjusting the resistance within a circuit, which is essential for applications such as speed control in motors or for modifying the brightness of lights.

When it comes to the operation of a transformer, rheostats are not typically utilized. Transformers work on the principle of electromagnetic induction and rely on alternating current (AC) and specific impedance characteristics for their operation. They do not operate effectively with variable resistance since their primary function is to convert voltage levels without changing the current significantly. Using a rheostat in this context could lead to inefficient operation or transformer damage, as a rheostat’s primary role is not suitable for high-voltage AC applications or maintaining the required voltage ratios.

Therefore, while rheostats find practical application in motors, resistance circuits, and heating elements, their use is least aligned with transformers, making this the most appropriate answer to the question.