A transformer is a device which is use to convert high alternatic voltage to a low alternatic voltage and vice versa.

Transformer works on the principle of mutual induction of two coils. When current in the primary coil is changed the flux linked to the secondary coil also changes. Consequently an EMF is induced in the secondary coil.

A transformer consists of a rectangular core of soft iron in the form of sheets insulated from one another. Two separate coils of insulated wires, a primary coil and a secondary coil are wound on the core. These coils are well insulated from one another and from the core. The coil on the input side is called Primary coil and the coil on the output side is called Secondary coil.

Suppose an alternatic voltage source Vp is connected to primary coil. Current in primary will produce magnetic flux which is linked to secondary. When current in primary changes, flux in secondary also changes which results an EMF Vs in secondary. According to Faradays law EMF induced in a coil depends upon the rate of change of magnetic flux in the coil. If resistance of the coil is small then the induced EMF will be equal to voltage applied.

According to Faradays law

Vp=Np DF/D t ------------ (1)

Where Np = Number of turns in primary coil.

Similarly, for secondary coil.

Vs = Ns DF /D t ------------ (2)

Dividing equation (1) by equation (2)

Vp /Vs = Np /Ns

This expression shows that the magnitude of EMF depends upon the number of turns in the coil.


There are two types of transformer:
Step up transformer
Step down transformer
A transformer in which Ns>Np is called a step up transformer. A step up transformer is a transformer which converts low alternatic voltage to high alternatic voltage.

A transformer in which Np>Ns is called a step down transformer. A step down transformer is a transformer which converts high alternatic voltage to low alternatic voltage.

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