Answer Posted / sarfraz

During the development of commercial electric power systems
in the late 19th and early 20th centuries, many different
frequencies (and voltages) had been used. Large investment
in equipment at one frequency made standardization a slow
process. However, as of the turn of the 21st century,
places that now use the 50 Hz frequency tend to use 220-240
V, and those that now use 60 Hz tend to use 100-120 V. Both
frequencies co-exist today (some countries such as Japan
use both) with no technical reason to prefer one over the
other and no apparent desire for complete world-wide
standardization.

Unless specified by the manufacturer to operate on both 50
and 60 Hz, appliances may not operate efficiently or even
safely if used on anything other than the intended
frequency.

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