A transformer is an electrical device that transfers energy between coils using a magnetic field. It is commonly used to raise or lower AC voltage.
How a transformer works
Most transformers have a primary coil and a secondary coil wrapped around a magnetic core. Changing current in the primary coil creates a changing magnetic field, which induces voltage in the secondary coil.
Why transformers matter
Transformers help power grids move electricity efficiently and help devices receive suitable voltages. In electronics, a transformer may be part of a power supply before rectification and regulation.
A transformer works with AC or changing signals, not with steady DC in the usual way.