My sister, who has a job similar to mine, sent me this link. Hope you enjoy:
10 everyday words that are often misused | Articles
Number 8? "Yea" is synonymous with "yippie"? "Yay" is, sure, but "yea" is actually synonymous to "yeah", isn't it? (Even if it's archaic.) And expressing one's joy by exclaiming "yeah" seems just as justified as doing it by exclaiming "yes", which is also done.