Certain transformer has full-load copper losses of 500 W. What is the value of the copper loss at half load

Certain transformer has full-load copper losses of 500 W. What is value of copper loss at half load:

1. 62.5 W
2. 125 W
3. 250 W
4. 750 W

Correct answer: 2. 125 W

Solution: Copper losses vary with the square of current.

Copper loss at half load will be:

(1/2)² * 500 = 500/4 = 125 Watt