Question

What is the appropriate and accurate way to find out the area vector ??? I know it is perpendicular to the surface ! But there can be two perpendiculars 1 upward n one downward ! So what is the method to find it out??? Help me out please

Answer 1

The way to find out, is using the so-called "cross-product". See:
-> http://en.wikipedia.org/wiki/Cross_product

(for a quick check, there's also the right-hand-rule..)

And as you already stated correctly, it depends on wheter you "turn" A towards B or B towards A..\[\vec A \times \vec B = - \vec B \times \vec A\]


Also note, that this is only true for right-handed coordinate systems! And for your own sake, I'd recommend to never _ever_ use something else! ;)