That is what bugs me a lot.Can you elaborate it more?
When you apply a voltage across an inductor, the current ramps upward. The higher the voltage, the faster it ramps up.
So on the rising part of the sine wave the current also rises, and the rate of increase gets faster and faster as the voltage increases up to its peak.
Once the voltage peaks at 90 degrees, the current in the inductor will be ramping up at its fastest rate.
Even as the voltage starts to fall off, the current through the inductor continues to increase (because there is still a positive voltage across the inductor), but the rate of increase starts to slow down.
In fact the current will go on rising as long as there is ANY positive voltage across the inductor. The result is that peak inductor current will occur just as the voltage falls back to zero, right at the zero crossing point.
The maximum rate of current change will be right at the voltage peak, because the voltage across the inductor is highest.
Maximum peak inductor current occurs just as the voltage returns to zero.
The result is that the current through the inductor lags the applied sine wave voltage by ninety degrees.