What type of device is commonly used to switch a motor on and off?

A contactor is a type of electromechanical switch that is specifically designed for switching electrical loads, such as motors, on and off. It is capable of handling the high current required to start and stop a motor, making it an essential component in electric motor control circuits. Contactors are typically equipped with electromagnets that actuate the mechanical contacts, allowing for reliable and efficient operation.

In contrast, resistors and capacitors serve different functions; resistors limit current flow, while capacitors store and release electrical energy but do not directly control the on/off state of motors. Transformers, on the other hand, are used to change the voltage levels in an electrical circuit but also do not perform switching functions for motors. Therefore, the contactor is the most appropriate choice for controlling motor operation due to its design and functionality tailored for that purpose.