It consists of two coils wound on the same core. The alternating current passing through the primary creates a continuously changing flux through the core. This changing flux induces an alternating emf in the secondary.
(1) Transfrmer works on ac only and never on d.c.
(2) It can increase or decrease either voltage or current but not both simultaneously.
(3) Transformer does not change the frequency of input a.c.
(4) There is no electrical connection between the winding but they are linked magnetically.
(5) Effective resistance between primary and secondary winking is infinite.
(6) The flux per turn of each coil must be same i.e.
(7) If NP = number of turns in primary, NS = number of turns in secondary VP = applied (input) voltage to primary, VS = Voltage across secondary (load voltage or output), eP = induced emf in primary; eS = induced emf in secondary, ϕ = flux linked with primary as well as secondary, iP = current in primary, iS = current in secondary (or load current).
As in an ideal transformer there is no loss of power
