Which device changes one form of energy to another?

The correct answer is the device known as a converter, which is specifically designed to change one form of energy into another. In various applications, converters can transform electrical energy to mechanical energy, mechanical energy to thermal energy, or even change the type of electrical current from AC to DC, depending on the specific function of the converter.

For instance, in beauty therapy and aesthetic treatments, converters can be utilized in equipment that requires different energy forms for specific procedures, such as laser machines that convert electrical energy into light energy for hair removal or skin treatments.

Other options, while they may serve important functions in electrical systems, do not perform the same broad function of energy transformation. A transformer specifically alters voltage levels of electrical energy, a rheostat regulates electrical current without transforming energy types, and an ammeter measures the flow of electric current but does not change energy forms at all.