What type of device is a transformer?

A transformer is fundamentally designed to change the voltage of electrical energy. It operates on the principle of electromagnetic induction to transfer electrical energy between two circuits through inductively coupled conductors. This voltage change can either step up (increase) or step down (decrease) the voltage level, allowing for efficient transmission and distribution of electrical energy over various distances.

Transformers are widely utilized in power systems to ensure that voltages are suitable for different applications, from high-voltage transmission lines to the lower voltages suitable for homes and businesses. This capability is crucial for minimizing energy losses that occur during electrical transmission over long distances.

In contrast, the other options describe functions that are not characteristic of a transformer. For instance, devices that convert electrical energy into mechanical energy would involve electric motors, while measuring electrical current pertains to ammeters. Additionally, transformers are not limited to use with direct current (DC); they primarily operate with alternating current (AC) due to the nature of their design and function.