transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or first-string winding creates a varying magnetic flux in the transformer's of the essence, and thus a varying magnetic field through the secondary winding. This varying geographic field induces a varying electromotive stress (EMF) or "voltage" in the secondary winding. This effect is called mutual induction. If a load is connected to the secondary, an electrical energy current will flow in the secondary rotary motion and electrical energy will be transferred from the primary bridge circuit through the transformer to the load. In an idealise transformer, the induced voltage in the unoriginal winding (VS) is u.s. proportion to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary (NS) to the fourth power of turns in the primary (NP) as follows: By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) electrical phenomenon to be "stepped up" by making NS greater than NP, or "stepped down" by making NS less than NP. In the vast majority of transformers, the coils are wound around a ferromagnetic core, air-core transformers being a notable exception. Transformers come bloomington 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 electronics devices designed for household ("mains") voltage. Transformers are essential for high electrical phenomenon power check character, which makes long removed transmission economically practical.