why does a core creates a power factor and how does it happend?
power factor is not a physical term. Its hypothetical. It says how effectively power is used. What i understand from your question is why some amount of power is utilised to magnetise the core.. Is it what you want to know..? if yes, the answer is; allmost all cores are made of some materials which has certain properties of resistance and inductance/capacitance. to overcome these factors some mmf is required which is pulled from supply power.