Question

hi,in ac current the terminals should change their poles (+,-) frequently,but in house wiring we only have one wire called hot or phase wire which has current ,another neutral,how?

Answer 1

There is as you say, one "hot" wire, but there is a companion wire called neutral, so there is two terminals (possibly 3 if you include the ground (greenj) wire). Between the two terminals the polarity will indeed alternate at the line frequency rate. In the U.S.A at a typical residence we would have a circuit similar to the drawing.