Right now, i'm stuck at finding the value of back emf. The following questions I think I can answer it. Since there is no value of armature resistance given, i cannot find the value of back emf using the formula Ea=V-IaRa. I am kinda newbie in this machinery subject, so, i dont know how to use the formula Ea=KΦnm. The attachment is the circuit i draw. Hope anyone can help me with this question.