[polipen]

Why do some countries work with 220 volts and others with 110 volts?
What are the convinience to use one or the other.

[Capuchin]

Why do some countries work with 220 volts and others with 110 volts?

Tradition, mainly.

What are the convenience to use one or the other.

In theory there are a few things, for example, incandescent bulbs designed for 120V are more efficient than those designed for 230V, whereas heating appliances can heat more with less conductor at 230V than at 120V.

However, in practice there is no real difference between the 2 systems, you can transform the voltage up or down at will easily.

[KISS]

I hope this isn't homework. There are ranges of voltages. For the US it's 120/240 for residential. The way the 120 is derived, it's safer from a shock hazzard point of view because a body typically gets in contact with one of the legs and ground or 120 V.

Businesses in the US may have 208 and 277 volts available and not 240.

240 or higher voltages have less wiring losses for high current appliances such as microwaves, toasters and hair dryers.

Some parts of Japan use 100 volts.

There is also 50 and 60 cycles per second. 50 Hz requires more iron in the transformer. Usually 50 Hz transformers will work on 60 Hz, but 60 Hz transformers may not. They will be marked 50/60 Hz.

60 Hz may have originated in the ability to keep time since 60 goes in evenly There are 60 cycles in a second, 60 seconds in minute and 60*60 seconds in an hour. The power lines frequency is contantly adjusted to maintain an average frequency of 60 Hz.

NTSC broadcasting used to be tied to this frequency until the addition of color. With ATSC broadcasting it's a divisor of the color bust crystal of 3.58.. MHz crystal and it's not quite 60 Hz.

PAL a standard used in Europe is based on 50 Hz.