Transformer

A transformer is a device that transfers electric energy from one cercuit to another throughinductive couples conductors — the transformer's coils. Except for air-core transformers, the conductors are commonly wound around a single iron-rich core, or around separate but magnetically-coupled cores. A varying current in the first or "primary" winding creates a varying magnetic feild in the core (or cores) of the transformer. This varying magnetic field induces a varying electrimotive force(E
MF) or "vlotage" in the "secondary" winding. This effect is called mutual induction.

If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will flow from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (V_S) is in proportion to the primary voltage (V_P), and is given by the ratio of the number of turns in the secondary to the number of turns in the primary as follows:

By appropriate selection of the ratio of turns, a transformer thus allows an alternating current(AC) voltage to be "stepped up" by making N_S greater than N_P, or "stepped down" by making N_S less than N_P.

Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids. All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for house hold voltage. Transformers are essential for high voltage power transmition, which makes long distance transmission economically practical.