What is an example of an autotransformer?

An autotransformer is a type of transformer that has a single winding that acts as both the primary and the secondary winding. This unique construction allows it to change voltage levels efficiently. In the context of the options given, one can see how both a voltage step-up transformer and a potential divider align with the characteristics of an autotransformer.

A voltage step-up transformer increases the voltage from a lower level to a higher one, which can be accomplished using an autotransformer due to its ability to tap into the winding at different points, thus boosting voltage efficiently with minimal energy loss.

On the other hand, a potential divider, which splits the input voltage into smaller output voltages, can also be implemented using an autotransformer. By tapping into the winding at various points, an autotransformer can provide multiple output voltages from a single input voltage.

This shows the versatility of autotransformers in both increasing voltage (as in a step-up application) and dividing voltage (as in a potential divider configuration), leading to the conclusion that both these applications are indeed examples of how an autotransformer can be used.