A transformer is a device that transfers electricity between two circuits by magnetic induction, according to the Nuffield Foundation. Transformers also increase or decrease the effective voltage as step-up or step-down transformers. A common use of an electric transformer is to convert the high-voltage electricity in overhead power lines into a lower-voltage connection suitable for home appliances.
A transformer consists of an iron core that is shaped like a ring, with one electrical circuit wrapped around each side but not directly connected. The magnetic flux created by the current flowing around the iron core transfers electric power to the other circuit. If the primary circuit has fewer coils wrapped around the core than the secondary circuit has, it transfers a higher voltage, stepping up the power provided. If the primary circuit has more coils than the secondary circuit, it reduces the effective voltage on that end. Transformers are important for reducing voltage, transferring high-voltage mains electricity into household current, then transferring that current into a lower-voltage supply for electronic devices. The electricity that flows into a home computer, for instance, may flow through a large number of transformers to alter the effective voltage, ensuring that all components receive just as much power as they need.