The home power, the one that goes into the electrical system of our homes is not continuous but alternating .    

This means that it changes its polarity continuously, that is, it flows first in one direction then in the other.    

For accuracy, the polarity changes at a frequency of 50 times per second.    

Using the frequency unit we can say that it is an alternating current with a frequency of 50 Hz ( HZ = Hertz ) and 220 - 240 V.

However, it is not so in all countries of the world, for example, in the United States, household power has a frequency of 60 HZ