How Transformers Work

Transformer is a tool used to raise or lower the alternating voltage (AC). The transformer consists of three main components namely: the first coil (primary), which acts as an input, the second coil (secondary), which acts as the output, and an iron core that serves to strengthen the magnetic field generated
When the primary coil connected to the alternating voltage source, changes in electrical current in the primary coil causes a changing magnetic field.

A changing magnetic field is strengthened by the presence of an iron and an iron core is delivered to the secondary coil, so that the ends of the secondary coil will arise emf induction.

This effect is called mutual inductance (mutual inductance)