A transformer is a power converter that transfers energy between two electrical circuits by inductive coupling between two or more windings. A varying current in the primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic flux through the secondary winding. This varying magnetic flux induces a varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is called inductive coupling. Wikipedia, Transformer
See Also
Electrical Transformer - 593128
Flyback Transformer
Induction
Law of Cycles
Law of Transformation of Forces
Principle of Regeneration