- A transformer is a static electrical device that transfers energy between two or more circuits through electromagnetic induction. It converts alternating current of one voltage to another voltage. - Transformers come in various sizes, from small devices inside microphones to huge units weighing hundreds of tons used in power plants. They operate on the basic principle that a changing magnetic field in one coil induces a voltage in another coil. - Transformers are essential for high-voltage power transmission, making long-distance transmission economically practical. They are widely used in both low and high current circuits and are found in many electronic devices.