Weighing Puzzle

PhiloLearner

Now you have 12 coins, one of which may be a fake. A fake coin has a different weight than a genuine coin, but you don’t know whether it is lighter or heavier.

Question:

How many weighings do you need in order to determine the identity of the fake coin, if any, whether it is lighter or heavier? and how ?

EDIT: sorry it's been posted before.