SSC JE Electrical Engineering 2012 Paper

Both hystoisis loss and eddy current loss gives rise to heart in a magnetic circuit. The two bosses are usually taken together and are called 'Iron loss'.
${\mathit{p}}_{\mathit{i}}={\mathit{p}}_{\mathit{E}}+{\mathit{p}}_{\mathit{H}}$
${\mathit{p}}_{\mathit{i}}={\mathit{f}}^2{\mathit{B}}_{\max }^2+\mathit{f}{\mathit{B}}_{\max }^{1.6}$
Iron-losses thus vary with both frequency and magnetic plux density. The power transformer is likely to be fed at the constant frequency and at the constant voltage, which means that magnetic flux density is almost constant. Thus iron losses in a transformer are constant from no load to full load.