Help finding direction of area vector on curved surfaces

[bfusco]

Homework Statement

I understand how to determine the direction on rectangular surfaces, however when it comes to a cylinder or sphere or, in the case of the problem i am working on now, for a long rod that has been bent around in a circle i.e a a rectangular ring, I don't know what to do.

 

[voko]

The direction of the area vector is given by the normal to the surface. At the curved side of a circular cylinder, that is simply the radial direction.