TABLE OF CONTENTS If we arrange two electrically isolated coils in such a way that the time-varying flux due to one of them causes an electromotive force (emf) to be induced in the other, they are said to form a transformer. In other words, a transformer is a device that involves magnetically coupled coils. If only a fraction of the flux produced by one coil links the other, the coils are said to be loosely coupled. In this case, the operation of the transformer is not very efficient.
In order to increase the coupling between the coils, the coils are wound on a common core. When the core is made of a nonmagnetic material, the transformer is called an air-core transformer. When the core is made of a ferromagnetic material with relatively high permeability, the transformer is referred to as an iron-core transformer. A highly permeable magnetic core ensures that (a) almost all the flux created by one coil links the other and (b) the reluctance of the magnetic path is low. This results in the most efficient operation of a transformer.
In its simplest form, a transformer consists of two coils that are electrically isolated from each other but are wound on the same magnetic core. A time-varying current in one coil sets up a time-varying flux in the magnetic core. Owing to the high permeability of the core, most of the flux links the other coil and induces a time-varying emf (voltage) in that coil. The...
