i tried figuring this out by a potentiometer but i burned it.........
This will happen whenever you use a potentiometer as a rheostat and don't use a fixed current limiting resistor as well. Your potentiometer had a relatively fixed voltage across it (the supply voltage less the forward voltage of the LED). Now look at Ohm's law for your rheostat (I = V/R). You had a fixed voltage divided by a variable resistance. As the resistance went down the current went up. Each time the resistance was halved the current doubled. What was the current just before the resistance got to zero? Answer: a lot (theoretically almost infinity). In your case the potentiometer burned out before the LED but it could have gone the other way or you may have hit the jackpot and destroyed both of them.
Don