The copper and iron losses of a 1-$\phi$ transformer are equal at 90% of full load and its value is 162 W. The total loss at 80% of full load is
Show Hint
To streamline this calculation without computing the full-load values explicitly, you can set up a direct ratio for the variable copper loss component:
\[
P_{cu}(x_2) = P_{cu}(x_1) \cdot \left(\frac{x_2}{x_1}\right)^2 = 81 \cdot \left(\frac{0.8}{0.9}\right)^2 = 81 \cdot \frac{64}{81} = 64 \text{ W}
\]
Adding the constant iron loss of 81 W gives the total loss of 145 W quickly and efficiently!