Reflection off Surfaces of Revolution: a Teachers' primer to the Introduction of the Cross-section Concept

The differential cross-section for the reflection of light beams off rigid bodies obtained by the rotation of a generic derivable convex function is calculated. The calculation is developed using elementary notions of calculus and is therefore suitable for calculus oriented introductory undergraduate university physics courses. Three particular cases are presented as examples of the general procedure and of the physical properties and considerations about cross-sections they allow to discuss in class.