How Does A Transformer Change Voltage?

Transformers are made according to electromagnetic induction. It consists of an iron core made of sheets of silicon steel (or silicon steel) and two coils wound around the core. The core and coils are insulated from each other and have no electrical contact with each other.
The coil connecting the transformer and the power supply side is called the primary coil (or the original side), and the coil connecting the transformer and the electrical equipment is called the secondary coil (or the secondary side). When the primary coil of the transformer is connected to the AC power supply, changing lines of magnetic force are created in the core.

Since the secondary coil is wound on the same iron core, the magnetic wire cuts the secondary coil, and the induction electromotive force must be generated on the secondary coil, so that the voltage appears at both ends of the coil. Since the magnetic field lines are alternating, the voltage in the secondary coil is also alternating. And the frequency is exactly the same as the power frequency.