Transformer works

The correct answer is Option (2) → on alternating current only

A transformer works on mutual induction: an emf is induced in the secondary coil only while the magnetic flux through it is changing.

An alternating current in the primary produces a flux that changes continuously, so an emf is induced in the secondary all the time. A steady direct current produces a constant flux, so no emf is induced (except for a brief moment when the current is switched on or off).

NCERT (2026-27):
Transformers – “For many purposes, it is necessary to change (or transform) an alternating voltage from one to another of greater or smaller value. This is done with a device called transformer using the principle of mutual induction.”

Transformers – “… When an alternating voltage is applied to the primary, the resulting current produces an alternating magnetic flux which links the secondary and induces an emf in it.”