Solution:

A step-up transformer reduces the current while converting low-voltage power to high-voltage electricity. High-voltage electricity is converted into low-voltage electricity by a step-down transformer.
As a result, a step up transformer is necessary to convert 12V a.c. to 200V a.c.
This transformer operates on the concept of electromagnetic induction. It states that the induced EMF in a conductor or coil is directly proportional to the rate of change of flux with respect to time.

Assume we have one winding that is powered by an alternating current. The alternating current that passes through the winding creates a flux. This flux is always changing or alternating and surrounds the winding. If any additional winding is brought closer to the preceding one, some of this flux will inevitably connect with the second. Because the amplitude and direction of this flux are always changing, there must be a change in flux linkage in the second winding or coil. There must be an EMF induced in the second, according to Faraday’s law of electromagnetic induction. There must be current flowing through the circuit of the later winding if it is closed. This is the most basic sort of electrical power transformer and the most basic of transformer functioning principles.