Transformers contain two coils of wires, one of which receives electricity at one voltage while the other usually puts out electricity at a lower voltage. The coil receiving an electric current emits an alternating magnetic field, creating a current in the second coil.
To reduce outgoing voltage in a transformer, the second coil must have fewer coils than the first. It can only use electricity with an alternating current, as a direct current does not create an electric current in the second wire. Transformers are essential to the electrical grid that powers homes and businesses because they change the extremely high voltages, forcing electric currents long distances into lower voltages safe for household use.