Final answer:
Transformers use Faraday's Law of induction, where a changing magnetic flux induced by an AC current in the primary coil generates an induced current in the secondary coil. The iron core increases the magnetic field strength, and the voltage induced in the secondary coil depends on the turn ratio to the primary coil.
Step-by-step explanation:
Transformers operate based on Faraday's Law of induction and the phenomenon of electromagnetic induction. According to Faraday's Law, a changing magnetic flux within an area enclosed by a conducting loop induces an electric current in the loop. Transformers consist of two coils, known as the primary and secondary coils. An alternating current (AC) input voltage is applied to the primary coil, which creates a time-varying magnetic field. This magnetic field, due to its alternating nature, induces a changing magnetic flux in the secondary coil. The iron core of the transformer serves to not only trap this magnetic field but also to increase its strength, analogous to a dielectric in a capacitor.
As a result of the changing magnetic flux through the secondary coil, an induced alternating current is generated in the secondary circuit. The voltage induced in the secondary coil can be either greater or less than the primary voltage, depending on the ratio of turns of wire in the primary coil to the secondary coil. This ability to transform voltage makes transformers highly useful in power transmission over long distances, as it enables the voltage to be raised to high levels to reduce energy loss and then lowered again for safe use in homes and businesses.