Question

Power transformer are designed to have maximum efficiency at -
1)Half load
2)No load
3)Near full load
4) Little more than full load

Answer 1

I think 4 I am not sure

Answer 2

Because only at full load are the total losses, including resistive losses, at maximum. If max efficiency was achieved at half load, then the additional heat generated by resistance and inefficiency between half and full load would overcome the ability to dissipate that heat, causing a fire.