why pakistan use 50Hz frquency rather then USA they use 60HZ once give the advantages and disadvantages?

Answer 1

The main advantages to 60 Hz. is that transformers are more efficient and motors run cooler.

Answer 2

Compatibility with the vast majority of the developed world. The same reason almost every country uses 220-250v mains too, which also allows around twice as much power per appliance.

The US, along with a lot of third world countries, is stuck with old fashioned low voltage mains power because their electrical standards are dangerous compared to those of Pakistan and most other countries.

There are a few countries that use 220v/60Hz.

Answer 3

There really isn't much of a difference either way. The range of 50-60Hz was necessary for lightbulbs (so the flicker fast enough that they seem solid to the eye). 60Hz was chosen because it fit in with the current time scale (60 minutes/hour, 60 seconds/min, 60cycles/second). Other than that, it was just arbitrary.