As inductor prevents the abrupt change of current so when dc current pass through the inductor there creates the rate of change of current.as well as rate of change of flux.so emf produced but this happen only for 5* time constant.after that there is no change of dc current inside the inductor and it acts a short circuit.so no emf produced.so why inductor at DC current acts as a open circuit at initial time and later as short circuit???
Try thinking of an inductor working with current the same way a big water wheel would act with a channel of water. At first the wheel's mass prevents it turning if there is a difference in water levels (voltage) on each side. Then it begins to turn and gradually speeds up until eventually it is turning almost as fast as the water itself is moving. At this point there is no difference in water level on either side on the wheel. The analogy is surprisingly close and this is because each has quantity that is reluctant to change. The key is that it is only reluctant, it doesn't refuse outright. So despite not changing its state instantly, like a resister, an inductor (or water wheel) does still begin to change even from the start. If the input conditions then remain static, then the inductor/wheel will eventually catch up (or get close enough anyway) and cease to provide any impediment to current at all.
extremely tough stuff. research on to google or bing. just that might help!
