Transformer is an electric device based on of mutual induction used to transfer power from the primary to the secondary by
convert low alternating voltage (at high alternating current) into high alternating voltage (at high alternating current) & vice versa without any transfer of charge. Its efficiency is defined as
k > 1 for a step up & k < 1 for a step down.
Because of energy losses like Flux loss, Cu- loss,
Fe – loss, Hysteresis loss, Humming noise, the efficiency of a transformer is never 100 %