What type of current is flowing on the main wires that connects to our homes?
is the current ac or dc? and why is that used instead of the other type of current?
AC, because it can be changed up or down in voltage through the use of a transformer. Otherwise, DC would be better. DC can be changed into a higher or lower voltage too, but not as easily and as cheaply as the transformer can do it. DC if applied to a transformer primary coil would simply magnetically saturate the core of the transformer, and thus could not induce a voltage in the secondary winding.