- A transformer is a static device that converts alternating current voltages to different voltages while keeping frequency the same through electromagnetic induction. - It works on the principle of mutual induction between two coils - an alternating current in the primary coil induces an alternating voltage in the secondary coil. - Transformers are used extensively in power transmission to increase voltage for long distance transmission lines and then reduce voltage for safe distribution, as well as in electronics to step down voltages for low-voltage circuits.