Efficiency is defined as the ratio of output power and input power. i.e. ‌‌η%=‌
p‌out ‌
p‌in ‌
×100 For an ideal transformer, p‌out ‌=p‌in ‌so,η=100% but in practical, efficiency of transformer lies between 70−90%. Given, V=200V,Ip=0.5A,Ps=100W We know that, Pp=Vp⋅IP=220×0.5 Pp=110W η=‌