A changing current in the primary induces an e.m.f. in the secondary. If the secondary is connected to a circuit then there is a current flow. A step-down transformer of 1,200 turns on the primary coil connected to 240 V a.c. will produce 2 V a.c.
hope this helps
a. magnetic field
A current carrying coil produces magnetic field and a changing magnetic field induces emf. In a transformer, when current flows in the primary coil, the magnetic field in produced which induces emf in the near by secondary coil. This results in current to flow in the secondary coil. There are two types of transformers- step up transformer has higher number turns in secondary coil and thus it steps up amount of induced emf. In a step down transformer, the number of turns in the secondary coil is less. So the induced emf reduces.
Hope this is the answer you were looking for and that it helps. :)
-- If the current is steady and unchanging, then smoke is produced.
-- If the current is changing, then voltage is produced between
the ends of the secondary coil of the same transformer.