A transformer is a static device which is designed to transform alternating current from one voltage to another through the process of mutual induction without any change in frequency shift. It is either used to bring up the voltage (step-up) or bring down the voltage (step-down) in AC electrical circuits.

Transformers do not provide electricity, but with the help transformer, the electricity is transmitted by magnetic coupling from one AC circuit to another. The transformer core with a regulated path is used to provide the magnetic flux produced by the flow of current that runs through the windings, often known as coils. 

The transformer uses two or more types of coils insulated wire with mutual connection, wrapped around a laminated steel core, each with hundreds or thousands of turns.

One coil is for electricity input called primary, which magnetises the iron core. The second coil is used for the electricity output called secondary or output coil. The voltage difference between the primary and secondary (or voltage ratios) varies on the turn ratio of the two spindles.

Transformers operate by following the law of Faraday, which states that the voltage ratio of two coils is equal to the number of turn ratio in the respective coils. Thus when a transformer needs reduced voltage, then the second (outgoing) coil would have fewer turns than the main (incoming) coil.