Question

a transformer is a device used for

Answer 1

A transformer is a device which is based on electro magnetic induction to raise or lower AC voltage

Answer 2

Transformer is a device which transfers electrical energy from one coil to the other. Only alternating current can be used and direct current cannot be used for this transformation. There are two types of transformers. One is step-up and the other is step-down. At the generation of electrical power first one is used to step up the voltage right from 660 to some 121.00 or so. In case of adapter what we use for operating electric gadgets we step down the house hold supply voltage 220 V to some 9 V or so
Transformers are used in many other electronic circuits such as "IF transformer" in case of radio equipment.