KEAM 2015 Physics and Chemistry Paper

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=‌

Ps

Pp

Efficiency of the transformer,
=‌

100

110

=0.9 or 90%