I should have paid more attention in school physics lessons!
Some countries in South America use Direct Current and if USA products are used there one must use transformers as you do here in the USA when using a battery oparated gadjet to a wall socket.This very Laptop I am using to communicate with you is battery operated and I have it plugged up to the wall to recharge as we speak(or type) and between the AC plug and my Laptop is a small rectangle that is transforming the AC current from the wall socket into DC current to the battery of the Laptop.
AC current carries frequency while DC current doesn't carry. AC current can be transmitted over long distances while DC cannot be done so due to the absence of frequency term.
DC is steady current, lile a car battery puts out-- always steady at 12 volts. Problem is, there's no way to change DC to another voltage. Which you want to do all the time, as various parts of, say, a TV need 1.1, 3.3, 5, 12, 15, and 300 volts. There are devices called transformers that change voltage, but they only work with changing voltages. If you put in DC, you get out exactly zero, as DC has no rate of change at all. Fortunately your simplest kind of rotating generator puts out a sine wave, which is the most congenial of waveforms. That's alternating current. Which is 100% compatible with transformers. So our power distribution system runs mainly on AC. (There is some advantage to using very high DC for long-distance lines )
