The effect of iron in distorting alternating-current wave form

It is well known that in a circuit containing no iron an impressed sinusoidal electromotive force will cause a sinusoidal current to flow, the current lagging behind the impressed electromotive force by an amount depending upon the relative values of the resistance and inductance, which in this case is constant. Assuming inductance alone in the circuit, the sine current which flows lags 90° behind the sine electromotive force and represents no power, the power-factor (cos 90°) being zero.