What does a transformer do?

A transformer is an electrical device used to modify the voltage of alternating current (AC). This is achieved through the principles of electromagnetic induction, where an alternating current in one coil (the primary coil) creates a magnetic field that induces a current in a second coil (the secondary coil). Depending on the number of turns of wire in each coil, a transformer can either step up (increase) or step down (decrease) the voltage.

The key aspect of a transformer is its role in adjusting voltage levels while maintaining the same frequency. This function is crucial for many applications, such as transmitting electricity over long distances, where higher voltages can reduce energy losses.

The other choices relate to different electrical devices or functions that do not pertain to a transformer's primary operation. For instance, increasing the current of direct voltage does not accurately describe a transformer's role, as transformers only handle alternating current. Storing electrical energy is typically the function of devices like capacitors or batteries. Lastly, while transformers might have some level of surge protection through construction, they are not primarily designed as safety devices against electrical surges, which is a function typically associated with surge protectors.