In electrical engineering, an autotransformer is an electrical transformer with only one winding. The "auto" prefix refers to the single coil acting alone. In an autotransformer, portions of the same winding act as both the primary winding and secondary winding sides of the transformer. In contrast, an ordinary transformer has separate primary and secondary windings that are not connected by an electrically conductive path. between them.
A variable autotransformer, with a sliding-brush secondary connection and a toroidal core. Cover has been removed to show copper windings and brush.
Variable Transformer - part of Tektronix 576 Curve Tracer
In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force (EMF) across any other coils wound around the same core. Electrical energy can be transferred between separate coils without a metallic (conductive) connection between the two circuits. Faraday's law of induction, discovered in 1831, describes the induced voltage effect in any coil due to a changing magnetic flux encircled by the coil.
An O-core transformer consisting of two coils of copper wire wrapped around a magnetic core
Instrument transformer, with polarity dot and X1 markings on low-voltage ("LV") side terminal
Core form = core type; shell form = shell type
Shell type transformer with laminated core showing edges of laminations at the top of the photo