Transformers are found everywhere alternating current is used. This includes both large power stations and the power cord for your laptop computer. A transformer is an electrical device that trades voltage for current in a circuit, while not affecting the total electrical power. This means it takes high-voltage electricity with a small current and changes it into low-voltage electricity with a large current, or vice versa. One thing to know about transformers is that they only work for alternating current, such as you get from your wall plugs.
How Transformers Work
Transformers use two coils of wire, each with hundreds or thousands of turns, wrapped around a metal core. One coil is for the incoming electricity and one is for the outgoing electricity. Alternating current in the incoming coil sets up an alternating magnetic field in the core, which then generates alternating current in the outgoing coil.
A “step-up” transformer turns low-voltage electricity into high-voltage electricity while dropping the current. Because high-voltage current can arc, step up transformers called ignition coils are used to power spark plugs. Dynamos at power plants generate large currents but not a lot of voltage. This electricity is stepped up to high voltage for transmission over wires, as electricity travels more efficiently at high voltage. A “step-down” transformer changes the 440-volt electricity in power lines to the 120-volt electricity you use in your house. Then, the current is either used at that level for devices like light bulbs, or it is converted to DC using an AC/DC adapter (the chunky thing at the end of your computer power cord that plugs into the wall), for devices like laptop computers.