Whenever i purchase earphone, the right earphone is louder than left. i tried it on various computers but result is same. are they manufactured in a way that right ear listens louder?

Are you certain that you are actually picking up/hearing "both" legs/ears properly, and not just one and the other is effectively just leaking thru? (This as in the jack plug is proplerly inserted into the socket each time?) It "may" be a "duff" pair you have... Try another pair in same sockets to confirm?

If you are trying different headphones on multiple computers it sounds like your hearing is off. If the same headset then look for an inline or individual volume controls on each ear. No they aren't manufactured to sound louder on one ear.

moonnightingale, try rotating either the headphones or your head 180 degrees and see what happens

if i swap them , then the left ear is louder. i dont know why. i mean the ear phone on which "Right" is written is always louder

Many possibilities here. Balance in the sound settings. Individual volume on the headset.

You imply that all headsets are like that. Mine aren't. 35 years ago I had a very expensive set of Pioneer headphones. They had volume controls right on the earcups.