The phenomenon in which an alternating current in one coil induces an emf in another coil is called the mutual induction.
Mutual induction of two coils depends upon the following factor:
Ø Number of turns of the coils.
Ø Area of cross-section of the coils.
Ø Closeness of the coils.
Ø Nature of the core material upon which the two coils are wound.
The transformer works on the principle of mutual induction between the two coils. A changing current in the primary winding induces an emf in the secondary winding.
Definition:A transformer is an electrical device which is used to increase and decrease given alternating voltage with out any changing in frequency.