Actually this not a question, I want to justify whether my concept is right or wrong. So lets start. Faraday's law of electromagnetic induction [itex]e=Nd\varphi/dt[/itex] explains the way of electromagnetic energy conversions. The induced voltage is always ac because the rate of change of flux is needed.As in transformer we give ac voltage and the induced emf in the coil is also ac . In dc motor though we apply dc supply voltage but again the induced emf/back emf/motional emf is ac? Am I right? Thanks for any replies.