DC & AC Electricity

We've known what is Electricity last contents.
Before talking about Motor, finally I would like to tell you about AC & DC Electricity.

DC Electricity has both poles "+" and "-", and the shape of frequency is always linear.
AC Electricity doesn't have any pole, but a sign frequency is moving.

You may have a question why AC Electricity has 2 leadwires.
The reason is Electricity should be operated through connected Electricity road.