Which term describes a transformer in which the primary and secondary are connected together in one winding?

• A. Arc
• B. Armature
• C. Autotransformer
• D. Bridge circuit

Answer: (C)

In an autotransformer, the primary and secondary share a single continuous winding on the core. The coil has a tap or taps that create the secondary voltage, while the input and load connect to different points on the same winding. One end of the winding serves as a common point, so part of the turns are used for the input and another part for the output.

Because both sides use the same winding, the voltage ratio is determined by the portion of turns between the common point and the secondary tap relative to the total number of turns. There is electric connection between primary and secondary, so there’s no isolation between them. This arrangement is compact and economical for small voltage changes, when isolation isn’t required. If isolation or larger voltage differences are needed, a two-winding transformer is preferred.

The other terms refer to different concepts: arc is a discharge phenomenon, armature is the rotating part of a machine, and bridge circuit describes a rectifier arrangement, not a transformer with a shared winding.