How the transformer works?

The transformer has two coils wound around the common magnetic core. When an alternating voltage is applied to the primary coil, the current flows through it. The current flowing in the primary coil produces the magnetic flux.

The magnetic flux produced in the primary coil is proportional to the ratio of the applied voltage to the frequency. According to Faraday's law of electromagnetic induction, the EMF is induced in the primary and as per the Lenz' law, the induced EMF always opposes the primary current that is responsible for begetting the EMF.
The voltage induced in the coil can be expressed by the following mathematical expression