∵ At maximum efficiency Iron loss = copper loss = 1000 W ∵ It occurs at full load, so full load Copper loss = Ifl2R = 1000 watt At half load, Copper loss =(
Ifl
2
)2×R=
1
4
Ifl2×R =
1000
4
=250‌watt So Copper loss at half of full load will be 250W. (Here Ifl = full load current)